Jason:

There is a product out called "torch down roofing" which very much resembles asphalt shingles, but comes in a roll (about 3 or 4 feet wide IIRC).

You simply roll out as much as you need on your roof and make sure it's not crooked, weigh down one end, roll it back up and then heat the bottom with a torch. When you do that, the material on the underside becomes sticky so that you just press it down and it sticks to the roof. This method is quickly becoming a favourite amongst flat roofing contractors because it's faster, easier and more reliable than a built-up roof. As long as the roof on your shed isn't so steep that you can't do that comfortably, then torch down roofing would be the way I'd go. Just start at the bottom and work your way up, just like with shingles.

So, instead of learning how to nail shingles down, I would investigate torch down roofing.