A Roof

1. The external covering at the top of a building.
2. The top external level of a building.
3. The upper part of a cavity.
4. (mining) The surface or bed of rock immediately overlying a bed of coal or a flat vein.
5. (rockclimbing) An overhanging rock wall

Both roofs and rooves are listed as plurals in the Oxford Dictionary of English, 2005 edition.

(cover at top of building): rooftop, tect (obsolete, rare), thatch

(in a cavity): ceiling