A roof is the top covering of a building. Flat roofs are often covered with tar and gravel and provided with drains to run off rain and snow. Variously shaped roofs are built to naturally shed water. These include straight, curved, and hipped styles. Some building styles, for example, geodesic and A-frame, blur the distinction between wall and roofs. Pitched roofs are often covered with asphalt shingles (in the US) although thatch, wood shake, steel, slate and tile roofs are common elsewhere. Newer systems include solar shingless which generate electricity as well as cover the roof.
Several systems of construction transmit the weight of the roof to the walls of the building and tie the roof into the structure. These include: king (queen) post, truss, rafter