Most residential metal roofs require at least a 3:12 roof pitch and have no maximum roof pitch. That means there is at least 3” of vertical rise to the roof slope for every 12” it goes back horizontally. That is a 14 degree angle. Mechanically seamed standing seam metal roofs, commonly used on large warehouses and the like, can be used on much lower roof pitches. Some homes may benefit most from two types of metal roofing on different roof planes to accommodate different pitches on the roof. Under no circumstances should a roofing product ever be installed at a pitch lower than that recommended by its manufacturer.