I had the 'opportunity' to re-roof my garage this summer, and I thought I'd try to save you from some of the trouble I went through.
Laying down shingles isn't really very complicated, as long as you have the right tools and the slope of the roof isn't too insane. If you've got a small area to cover, it's a reasonable project to take on. But forewarned: it's hard work. For a smallish garage (about 450 square feet of roof) it took me two full days (and I had help).
- Nail gun - don't do it without this, unless you're unusually dexterous with a hammer. I rented one at my local big-box hardware store for about $50/day.
- Shingle-cutting blade - it's basically a box-cutter with a curved blade, but it makes cutting through asphalt a lot easier.
- Pitchfork (or similar) for removing old shingles
Make sure you have some extra 2x4s around to use as stops (otherwise you'll be sliding down the roof with an nail-gun in your hand).
Do this job on a warm day (the shingles are easy to work with), but not too hot (they get wickedly hot in the sun).
Start laying down shingles in the middle of the roof and move out toward the edges (it makes it easier to correct your line if you get off track).
- Tear off the old shingles and replace any rotted boards. It is possible to roof over the old asphalt, but I don't think it's a good idea (and I know what I'm talking about, right? I did it once).
- Lay down felt paper and aluminum flashing.
- Lay down the shingles and nail them in, making sure the make a straight line.
- Don't fall off the roof or get a nail stuck in your thigh.
That's pretty much all there is to it. For a more detailed walk-through, check out this article.