the ceiling not displayed in 3D

The issue can happen if you have accidentally deleted the ceiling. If undo doesn't help, here are the steps how to re-create the ceiling: 1. Activate ceiling mode (there is a panel for that in bottom left corner) 2. Switch to 2D. 3. Left-click the room with missing ceiling. 4. In the popup toolbar select "Customize Ceiling" 5. Now draw the rectangle to cover whole room's area. 6. Exit this mode by clicking "Complete Ceiling" 7. Enjoy the resurrected ceiling! :)

I don't have a way to do this also, but It can be cheated by: 1. Make Extra Floor above it, and make small room only with the minimum height of Wall. 2. With the availability of this Floor, the Ceiling now can be visible. Hope it works.