The covering of the top of a building, or roof on project management , consists of three major components: The structural framing members a stiff membrane or roof deck Spanning structural members A waterproof outer layer of roofing The earliest roofing materials were probably mud and sod supported by logs and woven reeds. The early Greeks and Romans manufactured kiln dried clay tile to cover their public buildings and dwellings, clay tile is still popular. Bundle of straw or reeds tied to horizontal framing timbers formed the roofing for the thatched cottage in medieval Europe, and slate was used throughout the Middle Ages as a covering for the great cathedrals. By the 1500s copper sheets were pounded out by hand and used in limited quantities. After that time much of the slate and the roofing was replaced by copper, which is still widely used. Sheet lead has been used as a roofing material for centuries; a lead roof on the Hagia Shopia is still in good condition after 1,400...