So I was thinking about this today when I was talking about more than one roof. I think it's rooves, as weird as it sounds, because of other -f words that take -ve in the plural:

Wife > Wives
Leaf > Leaves
Dwarf > Dwarves
Half > Halves
Hoof > Hooves
Loaf > Loaves
Calf > Calves

Roofs also sounds weird. But I'm still not sure -- so what do you use?