The Roof Drain must be designed to drain off rain water in the most effective manner possible while maintain an aesthetic appeal. To select the proper roof drain, the following information must be determined: type of roof constructions, roof pitch, volume of expected rainfall, desired rate of drainage, roof load and safety overflow requirements location of drains and possible vandal proofing. For heavy rainfall regions, use 12″ diameter type and for light rainfall regions, use 8-12″ diameter type drains.