Ceilings

For the first time I was able to get the camera angle such that I could see open sky for my ceiling (including from the lower level of my 2-story house). I did a search on ceilings and this is the only thread I could come up with that had an answer for how to add them. However, I can't get this to work. No matter where I click, I can't get a "yellow line" to show up. All I get is a white line surrounding the room, and this is true regardless of which floor I am on. No where does an option to "build ceiling" come up. Am I doing something wrong? I'm wondering if the lack of ceilings I specifically put into place is the reason my sprinklers didn't work last time I had a fire. Seriously, a ceiling should just be added automatically when adding a second level or a roof. If not automatic, it should at least be obvious how to do it yourself. This is irritating.

ETA: Hmm, never mind... I think. I had the walls cut away when I did this last time. With the walls fully up, it is very difficult to get a view where the ceiling is visible because you can't look up from horizontal, but I was just able to see a bit of a corner of a ceiling. Still doesn't explain why the sprinkler didn't work.