Originally Posted by Supratad:
“The roof of the Pantheon is solid concrete, as are many modern buildings, so in those cases the ceiling and the roof are one and the same.”
It's one piece if someone says "the roof fell in" or "we need to remove the roof" but if someone asked me to "paint the ceiling" I would arrange to paint the inside, not the outside. And if I was asked to "get up on the roof" I would climb up on the outside, not try to work out some way to cling Spiderman style to the ceiling.
Cracks on the ceiling means you can see it when standing inside, a cracked roof means you would have to go outside to have a look.
If I was sitting in a room and someone said a hang glider had landed on the roof, I wouldn't just look up and expect to see it above me...unless it was a glass ceiling of course.