Originally posted by knighttemplar1960:

I've never been able to use a stone floor as a roof either as the stone floor tiles do occasionally need repair.

I have a huge fortified compound with two all-stone gatehouses and six all-stone towers, all using stone floor tiles for roofs. I've never once ever had this problem in over 800 in-game days. The only time the stonework has ever needed to be repaired is when the greydwarfs in the neighboring black forest run out to smack the walls or if they get damaged from raids.