Can I make a mesh, say 400x400x20, then put a floor material on one side and a ceiling material on the other? Would the thickness (20) need to be greater?
Sure. In your 3d app apply to the sides of your box (cube) six different materials.
For each side one.
Thickness is relative.
20mm 20km…
Check against ingame existing assets (playerchar(184cm)height).
