gallonsquare feet. Other websites say a gallon will cover 400-450 square feet of smooth surface. If you've got a rough textured surface or surfaces which need 2 coats of paint, a gallon will cover about 200 square feet. The above answer may be a general rule of thumb.
Highly rated roofing contractors tell us that asphalt is the most affordable roofing option, followed by wood, tile, metal, and slate. Materials for a metal roof can cost up to $350 to $1,500 per 100 square feet. Angie's List members recently reported paying an average of $12,236 for a metal roof installation.
1 Metal roofing materials cost about $1,000-$2,000 for a single-wide or $1,800-$3,000 for a double-wide, depending on size of unit and manufacturer and are designed to last a lifetime.2  Metal roofs may be installed over an existing roof with or without a DIYer adding insulation in between. Composition shingle roofing is typically added to a pitched roof that repels water better than its flat counterparts and costs about $650-$2,175 for materials for a single-wide or $1,290-$4,250 for a double-wide, depending on size of unit, thickness or quality of shingle and location.