Commercial roofing is sometimes described by the type of roof on the building: flat, low slope, shed and steep slope, for example. In other cases, roofing is described by the installation technique - such as "built-up roofing," "standing-seam roofing," "single-membrane roofing" and "torch-down roofing." More frequently, roofing is described simply by the material that's being installed. Here are brief descriptions of the main commercial roofing materials being used today: