Looking good Mopz.
Can you have rooms over rooms or is there just the one ground?
As you may have guessed it's all quite limited.
It's grid based, just like the raycaster things. For each cube you can set four walls, a ceiling and a floor, and you can split it diagonaly. The differen parts of the cube aren't "connected" to eachother. In combination with a heightmap (almost all the floor, not only the outside dirt, in the video is part of the heightmap), you can have a maximum of two floor levels.
I'm sorry about the limitations, but it's an old engine
Atleast it's easy to create maps