You build out walls and stairs, line them up in UE, and the corridor is too narrow. You build a watchtower and, on climbing it, cannot see much. A level's shape can feel different when you move a player through it than when you look at it in the editor.
So build the rough shape from boxes and stairs first and walk it. That step is greyboxing . UE5's Modeling Mode lets you build and test shapes without going back and forth to external software like Blender.
This article starts with a small platform made from a box and four steps. Once you confirm you can climb it, raise it and add walls to extend toward something like a watchtower.
What You'll Learn
- Why you test a level's shape before building out the look
- The flow of creating, accepting, and saving shapes in Modeling Mode
- Checking dimensions against the player's size and collision
- Hands-on: build a platform you can climb with four steps
Greyboxing is a draft of the playable shape
Greyboxing is the step of assembling a level from simple shapes to check how it plays. It is also called blocking out. Grey boxes are common, but coloring shapes to tell them apart is fine.
For a corridor you flee enemies through, you test "is the corner easy to turn"; for a high platform, "what do you see once you climb". Dimensions are not the only thing that makes something fun, but how long movement takes and how the surroundings read do change with width, height, and distance .
While shapes are simple, changes such as "widen the corridor a bit" or "move the platform away from the wall" are easy to try. The aim is settling the foundation of walking, jumping, and looking around before adding decoration.
Open Modeling Mode
Modeling Mode is the mode for creating and editing 3D shapes inside UE. Data representing a 3D model's shape is called a mesh .
- Choose "Modeling" from the mode selector at the top of the level editor (normally "Select Mode"). The shortcut is
Shift + 5. - If the entry is missing, find "Modeling Tools Editor Mode" under "Edit → Plugins" and enable it. Save and restart if prompted.
- Once the tool list appears, find the "Create" category. The tools for basic shapes are there.
To return to normal selection and placement, use "Select Mode" or Shift + 1 . Tool names and panel layouts differ slightly between UE versions.
Create, accept, and save shapes
Three tools are enough at first. UE's standard length unit is cm, so a width of 200 is 2 m.
| Tool | Shape it makes | When to use it |
|---|---|---|
| Box | A box, specifying width, depth, and height | Floors, walls, platforms |
| Cylinder | A cylinder, specifying radius and height | Pillars, round platforms |
| Stairs | Stairs, specifying step count, step height, width, and so on | Paths up to high places |
A Cylinder's radius is from the center to the outside. Stairs' "Step Height" is the height of one step , not the whole staircase.
Choosing a tool previews the shape being created. Once dimensions and position are set, Accept confirms it. Cancel discards the operation. Even with a shape visible on screen, creation is not finished while it is still a preview.
We set "Output Type" to Static Mesh here, a mesh saved to the Content Browser and reusable elsewhere. There is also a "Dynamic Mesh" option, but this article stays on Static Mesh.
After accepting, save both the mesh asset holding the shape and the level holding the placement . By analogy, the mesh is the part for placing the same shape many times and the level is the layout arranging those parts. You can confirm the generation destination in Modeling Mode's "Quick Settings" and similar. Rather than relying on the default location, gathering them in a practice folder makes them easier to find later.
Creation settings do not persist after accepting. Selecting an accepted staircase does not let you change "step count" whenever you like. To rebuild a shape, use Stairs again or the editing tools below.
Use the player as a ruler
When judging whether a corridor is passable, look at the capsule rather than just the human-shaped visual. The Third Person template's player is a Character with walking and jumping features. A Character uses a capsule-shaped collision volume to contact walls and floors.
Open the player's Blueprint and select "Capsule Component" to see the shape and dimensions. "Capsule Half Height" is half the total height and "Capsule Radius" is the radius. At Scale 1, the total height is twice Half Height and the width twice Radius.
| What to check | Its relation to the player |
|---|---|
| Corridor width | Not just whether the capsule fits but whether turning has room |
| Floor-to-ceiling height | Whether your head clears while walking and jumping |
| One step's height | Whether it is reasonable against Character Movement's "Max Step Height" |
Max Step Height is the maximum step a Character can walk over. It is a separate setting from the capsule size, on the "Character Movement" component (see the Character Movement article).
A step lower than that value is not guaranteed climbable, though. Invisible collision blocking it or a gap against the platform also stops you. Check dimensions and collision, then finish by actually walking it. In third person, the body may fit while the camera crowds the wall and hurts visibility.
Hands-On: build a climbable platform with stairs
Try it in a Third Person template level where the player can move. Place a box platform and stairs on the existing floor; success is reaching the platform's top by walking, without jumping .
1. Prepare a practice level and save location
- Create a
Content/Greyboxfolder in the Content Browser. - Save the current level into that folder as
L_GreyboxPracticewith "File → Save Current Level As". - Open Modeling Mode and confirm the generated mesh save location in Quick Settings. Point the specifiable destination at your practice folder.
- Choose a wide open spot on the floor. Put the Player Start on the floor, clear of the platform you are about to build.
The Player Start marks where the player begins the game. Buried inside your prototype, it trips you up before you can test climbing.
2. Build the platform with Box
Choose "Create → Box" and set Output Type to Static Mesh. Use these width, depth, and height values.
| Setting | Value |
|---|---|
| Width | 400 |
| Depth | 400 |
| Height | 80 |
Click on the floor to place it and align the box's bottom to the floor's surface. Adjust the height with the move gizmo if needed and confirm with Accept. Leave this Actor's Scale at (1, 1, 1) . Changing Scale too makes the entered dimensions differ from the visible size.
Naming it Greybox_Platform in the Outliner makes it easier to select later. That is the name of the Actor in the level, set separately from the mesh asset's name in the Content Browser.
3. Build four steps with Stairs
Choose "Create → Stairs" and build with these settings. Output Type is Static Mesh here too.
| Setting | Value |
|---|---|
| Stairs Type | Linear : straight stairs |
| Number of Steps | 4 |
| Step Height | 20 |
| Step Width | 200 |
| Step Depth (one tread) | 40 |
Climbing four 20 cm steps puts the top step 80 cm above the floor. Align the stairs' base with the floor and the top step with the platform's surface. Viewing from the side makes height offsets and gaps easy to spot. If the stairs face the wrong way, rotate them into place and confirm with Accept.
Back in normal selection mode, W moves and E rotates. Name the stairs Greybox_Stairs and, after checking the seam, save the changed meshes and the level.
4. Prepare collision
Collision is the hit volume. A mesh's appearance and the shape the character contacts are set separately. Results vary with creation settings, so "the stairs are visible" does not mean you can climb them.
Here we use a few simple shapes as immovable platforms. As a straightforward approach, we use the mesh's own faces as collision.
- Select the platform Actor and open the mesh in use from the Static Mesh field in "Details". Double-clicking that mesh in the Content Browser also opens it.
- Find "Collision Complexity" in the Static Mesh editor's Details and set it to Use Complex Collision As Simple .
- Save the mesh. Apply the same setting to the stairs mesh.
- Back in the level, set the platform's and stairs' Actor "Collision Presets" to "BlockAll". Leave "Simulate Physics" off.
These settings suit this exercise's static walls and floors. For objects rolled by physics or many detailed shapes placed at scale, build simple collision suited to the use.
5. Climb it, then compare different widths
Save the level and Play, then walk up from in front of the stairs. Walking on the platform and turning without falling through means it works for now.
Next stop Play, build new Stairs with only the width changed to 100 , and connect them to another edge of the same platform. Keep the step count, height, and depth the same and configure collision. Walking both shows the difference between a width you can walk straight up and one that makes turning or sidestepping easy.
Changing one condition at a time like this makes it easier to find dimensions suiting your game. The width you choose also differs depending on whether you want a narrow staircase as a risky shortcut or a wide one as a place to fight.
| Problem | Where to check first |
|---|---|
| You pass through the box or stairs | The mesh's Collision Complexity and the Actor's Collision Presets |
| You stop in front of a step | The collision shape, one step's height, Character Movement's Max Step Height |
| Only the last step is unclimbable | The platform surface's and top step's heights, gaps at the seam |
| The shape is larger or smaller than expected | The creation dimensions and the placed Actor's Scale |
| Editing one shape changed another | Whether they use the same mesh asset |
That last case happens when several Actors use the same part. Duplicating an Actor in the level does not make the mesh asset a separate one. To edit one shape alone, duplicate the mesh in the Content Browser, assign the duplicate in that Actor's Static Mesh field, and then edit.
Once comfortable, extrude faces and cut holes
Boxes and stairs alone let you test corridors and elevation quite far. Once you want windows and relief, add shape-editing tools.
PolyEdit: select faces and change the shape
PolyEdit (PolyGroup Edit) edits by selecting groups of a mesh's faces. A mesh is a collection of small triangles, but handling them as groups lets you operate on a box's side face as a unit.
- Extrude : pushes selected faces outward. Used for adding a protrusion to a wall and the like.
- Inset : creates a slightly smaller face inside a face. Used to prepare edges and frames.
Select the mesh to edit and operate on faces with PolyEdit. Check the shape in the preview and confirm with Accept. Extruding a box's whole top face does not produce a hollow room. For a first room, arranging thin Boxes as walls is easier to assemble.
Boolean: cut a hole using overlapping shapes
Boolean edits by adding or subtracting using two shapes' overlap. To cut a window into a wall, subtract a small box's volume from the wall.
- Prepare the wall Box as A and a small Box shaped like the hole as B. Overlap B so it passes through the wall's thickness.
- Select wall A, then small box B, and open the Boolean tool.
- Choose "Difference A − B" and check the preview with the hole in the wall. If the wrong thing disappeared, check the order of A and B.
- Confirm the output destination and whether to keep the original A and B, then Accept. Duplicate original meshes you want to keep before practicing.
After cutting a hole, check collision too. Even with a visible hole, simple collision covering the whole wall keeps you from passing. Test the hole's purpose as well: sightlines for a window, a walkway for a doorway.
Bonus: where to go once the shape is settled
Keep walking it after the look is finished. Swapping in Fab assets or your own models can narrow corridors by the width of pillars and decoration. Using the greybox dimensions as a reference, walk the same route again after swapping. Prototype meshes can be replaced entirely or refined and kept.
Match the tool to what you are building. Landscape helps with mountains and wide ground, and Modeling Mode with structures made from boxes and stairs. Complex models such as characters can be built in combination with Blender and the like. You do not have to complete every step inside UE.
Extend toward a tower or a path through your game. With a small platform working, add walls and railings with Boxes and vary the height. Placing a coin from the coin-collecting game at the top lets you test whether it is "a place worth detouring for".
Summary
Greyboxing means building simple shapes and moving through them to check space and height. Modeling Mode lets you test right there, starting from building a box and stairs.
Confirm shapes with Accept and save the meshes and the level. Once collision is prepared and you can walk it, change width and height one at a time. Keep stacking small experiments that take you from "climbable" toward "easy to climb" and "worth climbing".