Each length of roofing sheet metal—called a pan—must be bent up at the edges to make seams. Thoughtful planning of the layout and careful measuring of the materials will help make an attractive, smoothly executed installation in the long run. Sketch the layout of your roof, calculating for symmetrical seams and avoiding awkward or unusually narrow pans. Many old-house roofs are built with less than even dimensions, so be prepared to work your layout from the middle of the roof to split up any odd spacings. If you will be making seams along ridges where two roofs meet, remember to offset the pan spacing so that the seams in one roof meet the center of the pans in the other roof. This way, you won’t have too much metal to bend into a uniform, tight ridge seam.
To make pans, measure from 4″ above the roof ridge (to allocate metal for a seam) and 1″ beyond the roof edge, then cut your metal to this dimension with metal shears or tin snips. Next, bend up the long edges of the pan, 1½” on one side, 1″ on the other. (On a simple gable roof, the outboard first and last pans will have one edge—the one that runs along the roof rake—bent down 1″ so it can be crimped to the drip edge or locking strip.)