Level Blockout and Greyboxing: Design Your Level Before You Buy a Single Asset

Every dev does this at least once. You open the engine, drop in a terrain, spend three evenings placing trees and lamp posts, and then discover the level plays like a hallway with extra steps. The layout was never tested, only decorated. And now every fix means moving fifty carefully placed props. Level blockout, also called greyboxing or whiteboxing, is the habit that stops this from happening. You build the entire space out of dumb grey boxes first, walk it, jump around in it, break it, fix it, and only then spend money and hours on art.

Studios treat this as non negotiable. There is a whole community tradition, Blocktober, where AAA level designers post their raw blockouts every October, and the striking thing is how good those levels already look as pure geometry. The fun was built before a single texture showed up.

What a blockout actually is

A blockout is a playable rough draft of your level made from primitive shapes. No materials beyond a grid texture, no props, no lighting pass. Just floors, walls, ramps, stairs, and cover, at the correct scale, with a real player controller walking through it.

The point is cost. Deleting a grey box costs nothing. Deleting a room that took two weeks of modeling, texturing, and light baking hurts, so you will not do it, and your level stays worse than it should be. The blockout phase is the only time in production when big layout changes are cheap, so the goal is to make as many of them as possible while they still are.

The tools, engine by engine

Unity: ProBuilder

ProBuilder ships as an official package (version 6.x for Unity 6) and it is still the default answer. Boxes, ramps, stairs, and poly editing right in the scene view. Install it from the Package Manager, stick to simple shapes, and resist the urge to model anything pretty with it. If you want a scale reference and have nothing else, a default capsule is 2 units tall and 1 wide, which is close enough to a person to be useful.

Unreal: Modeling Mode and CubeGrid

UE5 has this built in. Modeling Mode includes CubeGrid, a push and pull grid tool that feels like sculpting with LEGO and is absurdly fast for blocking rooms and stairs. If you want more comfort, the third party Blockout Tools plugin (currently v1.52, supporting UE 4.22 through 5.7) adds 15 primitive types like doorways, railings, and curved stairs with a triplanar grid material already set up.

Godot

CSG nodes (CSGBox, CSGPolygon and friends) are made for exactly this. They are slow at runtime, which does not matter at all for a blockout you will replace anyway. Community tools like Greyboxer can also export blockouts to .glb with collision included.

The numbers that keep your level honest

Scale is where most first blockouts fall apart. Rooms feel like warehouses, doors feel like cat flaps, and nobody can say why. The fix is metrics: a small set of dimensions you commit to before you build. The Level Design Book, a free reference every level designer should have bookmarked, collects the common ones. For Unity (meters): player capsule about 1.0 x 1.8, eye height 1.5 to 1.7, interior walls 3.0 high, hallways at least 2.0 wide, doors around 1.25 x 2.5, stair steps 0.1 high and 0.15 deep. For Unreal (centimeters): the default mannequin capsule is 60 x 176, doors around 110 x 220, halls 150 minimum.

Two things worth knowing about these numbers. First, they are deliberately bigger than real world architecture, because game cameras and game movement make realistic rooms feel cramped. Copy a real floor plan exactly and it will play terribly. Second, they are starting points, not laws. If your game is about being small, or fast, or claustrophobic, bend them on purpose.

Blockout geometry is cheap to delete. Art passed geometry is expensive to delete, which means in practice you never will.

Grey boxes should not actually be flat grey

Flat untextured grey kills your depth perception. You lose all sense of distance and scale, which defeats the purpose of walking the space. Use a world aligned grid or checker texture with lines at regular intervals, so every surface tells you how big it is at a glance. The clean way to do this in Unity or Unreal is a triplanar material: it projects the grid in world space, so you never touch UVs and every box you drop is instantly readable. Unity's Shader Graph has a built in Triplanar node, and Unreal's material editor has WorldAlignedTexture. Ten minutes of setup, permanent payoff.

Playtest before you decorate

A blockout you have not walked through is just a diorama. Get a player controller in on day one and test constantly. Does the jump you planned actually clear that gap? Can you see the objective from the entrance? Do fights have enough room to strafe? Watch someone else play it too, because they will immediately walk to the one place you never considered and fall through the floor.

Studios formalize this with a metrics test map, sometimes called a metrics zoo: one dev only level containing every standard element (halls, doors, stairs, jumps, cover heights) so changes to movement can be sanity checked in minutes. For a solo dev this can be one small scene you keep forever. It is twenty minutes of work and it will save you from rebuilding levels after every character controller tweak.

When to stop blocking and start buying

The blockout is done when the level is fun with no art in it. That is the bar. If the space is boring as grey boxes, art will not rescue it, just hide the problem until reviews find it.

Once the layout is locked, the art pass gets much cheaper, because now you know exactly what you need. Your blockout dimensions become a shopping list: so many wall segments, so many door frames, stairs at the step height you tested. That is exactly the situation where a modular environment kit earns its price, since kit pieces snap to the same regular dimensions your blockout already uses. And if this is your first project, we wrote a guide on which assets are worth buying first so the budget goes where it matters. When you are ready to swap boxes for real meshes, marketplaces like DevLoot are the art pass, not the starting point.

A Unity graybox in progress, capsules as scale references. Image by Robert Yang, via Radiator Blog.

One last push: do not polish the blockout. The moment you catch yourself beveling a grey box or tweaking its material, stop. Ugly is the feature. Ugly is what makes it disposable, and disposable is what makes it powerful. Block it out, walk it, fix it, and only then make it beautiful.