Galvanized Roofing angle cutting

Hi, I am putting a galv roof on a gazebo for myself and am really having problems figuring the angle cutting as it is a triangle pointed roof on 4 sides. Does anyone know of a good tool for angle roofing cutting. I have 4 sided triangles on roof with a 5/12 pitch on top of 12X12X 8high gazebo. (it has 4 sides coming to point on tip of roof. Or any good ideas for layman??? Much appreciated. I may be able to get picture downloaded later.