There is no straight answer to this question. It depends on the type of roof (shingle, tile/metal/flat). Metal roofs are the most expensive, but you get the bang for your buck- they last up to 50 years, and are the most hurricane resistant. Tile roofs are the next most expensive, and fare greater with foam adhesive than nailed-on or screwed-on tile. Followed by shingle & flat roofs which are the least expensive.