Hey JellyFish, thanks for all of your feedback! I appreciate you trying out the demo
You can hide roofs using the X key, or clicking the icon on the left side of the screen with the walls and roof.
Basements and attics will be added in the future!
Indoor windows are not possible yet, due to the way the GPU processes graphics, it requires extra work to make partially see through textures draw in the proper order on screen.
I'll add a over-mouse message stating what delete mode is active, if that's what you mean?
I'll also add clearer instructions on how to create a mixed used building. Basically you need to choose a building type, then click on the room menu icon and place the room in the zone.