roof, covering of the top of a building, serving to protect against rain, snow, sunlight, wind, and extremes of temperature. Roofs have been constructed in a wide variety of forms—flat, pitched, vaulted, domed, or in combinations—as dictated by technical, economic, or aesthetic considerations..

• Flat roofs came into widespread use
• Sloping roofs come in many different varieties
• external covering of a roof must prevent rainfall or other precipitation.
• waterproof membrane or film that is applied as a liquid and that repels water .
• pieces of a waterproof material that are arranged in such a way as to prevent the direct passage of water