Nice house [:)] As long as ceiling is checked, it is understandable that the beams are invisible as they are above the ceiling.

I cannot deactivate the ceiling.

This is the strange part. Are you sure there are not several rooms on top of each other? Could you by accident have double-clicked with the room tools several times? (Or a room with ceiling on a lower level?)

Just a hunch, but I would certainly try to delete the room(s) and double-click to put the room back in (without the ceiling checked).

ok