Flat roofing is the most common type of roofing and comes in a variety of shapes and designs. The vast majority of flat roofs are made from asphalt, which is waterproof. They also provide good insulation qualities, meaning they can keep the house warmer in winter time or cooler when it gets warmer outside. Ridge width is the distance between the inside and outside of a roof. The ridge width can be determined by measuring from rafter to rafter (outside to inside) as well as the overhang, or how much of the roof extends below the eave line.