Won’t let me build a ceiling and my “room

@nakotacola Did you try going to the link to also view screenshots of the process? When you click the room wall does the whole room highlight or just the one wall? If the whole room doesn't highlight when you click one of it's walls, you may be dealing with an incomplete room... one that the game is not seeing as a room. If this is the case, try retracing all of the walls on the room with the wall tool until you get all the way back to connect to where you began. You should then hear a faint 'thunk' sound, and see a faint dust animation to tell you the room has been made. This will likely create the ceiling automatically, but if it doesn't, click one wall to confirm that the game then highlights the entire room, and try again on the 'build a ceiling' process.

If worse comes to worse you can copy the entire room and go up a level and paste it exactly above it (or draw an exact copy exactly above it in the floor above), then confirm that the floor for the room above has closed the room below with it's floor, then delete the walls and the ceiling of that room on the floor above if you don't want a room up there.