Out of curiosity, which light were you trying to place, the overhanging ceiling lights or wall lights? I downloaded a house with some dance floors on the roof, which made a pretty cool skylight, I didn't bother to replace the ceiling lights as I liked them, but I had no problem placing any other kind of other light.
I did have one weird glitch that happened, I accidently deleted the bedroom window before saving and didn't notice until after I had gone back into the game. There was a big empty square where the window used to be, like someone had just cut a square hole in the wall.
Replacing the wall didn't make it go away, nor did building a new one, the only thing that work was replacing the window. Such a strange glitch, I am wondering if this is also caused by the dance floors but I'm pretty sure I have a different one from you guys, mine is a glass tiled one. I can look it up and post the name if it helps anyone?
I'm having no issues with my dance floor ceiling or as I like to call it, Disco Roof.
I'll let you guys know if I do run into problems though.