Hi all. I just started installing sheet metal roofing (Skyline 16'' wide) on a house which has 2 gable dormers. I snapped my line in the valley, 4'' out of center and made a jig to clamp to the metal and used a metal stud saw blade to cut a clean line. The problem was figuring out what the angle was. Now I know there are many smart builders who must have figured out a trick to this. My main roof & dormers are 6/12 pitch. Any ideas?