Determining length of roof panels

Is there a formula for figuring how long the separate panels need to be? The supplier will cut them to size. It's for a 1:12 pitch over a 8'-7" span with a 12" overhang.

Easy Answer: 9'7-1/2" (depending on the type of panel, you may need to add some for overhang) Harder, More technical answer: A 1:12 pitch means that for every 12" across, the roof rises 1". (8'-7" + 1') = 115" across (115" * 1/12) = 9.5833" rise Then by using the Pythagorean Theorem, we can figure the slope (115*115=13225) + (9.5833*9.5833=91.84) = 13316.84 then (square 13316.84) to get 115.4" = 9'-7.5"