A roofing system is an assembly of interacting components designed to weatherproof the roof surface of a building. Typical roofing systems are a "hodge-podge" of different manufacturer's components. For example, your shingles will come from one manufacturer, your underlayment from another, your ridge-vent from another, and so on. Atlas does not recommend THAT kind of roof. The Atlas Signature Select™ Roofing System is designed to put all Atlas components on your roof, giving you one source for roofing materials, one place to call if you ever have a problem and DOUBLE the Premium Protection Period (see limited warranty for details).