I should start an informal poll on how many users have created multiple ceilings in a room because the Auto Ceiling function does not discriminate against multiple ceilings in the same location. When you try to put other elements in the same location as another Revit howl's in pain but not the ceiling tool. It's says, "Go for it dude...make as many as you like! It'll just confuse you later and it'll be like..kewl...I'm so like sitting back here and chuckling at you!"
I think something like twenty was the worst I've encountered. It goes something like this..."Steve, why can't I delete this ceiling?" I use a crossing selection window and filter out the other elements and find 20 ceiling elements. I tell them they placed 20 ceilings and they WERE deleting them just not ALL of them. I then wonder how many he deleted and how many there were originally?!?
He says,"How did I do that...oh wait? I placed the ceiling but I didn't see it at first so I tried again, and again and again and again..." This happens the most with the GWB ceiling type that doesn't have a material assigned to the GWB which means you can't "see" it. You aren't convinced there is a ceiling so you keep clicking! Remember a definition of insanity is doing the same thing repeatedly expecting different results.
I'd like the ceiling tool get a bit smarter, a bit more discriminating. Which reminds me the ceiling tool ought to be able to detect columns just like rooms!!