I haven't tested this long term but it seems to work on my chicken coop. Here's the rundown:
Using scissors or tin snips cut the ends off an aluminum soda/beer can and cut down the middle of the can to make a flat rectangular piece of aluminum. Then you lay the flat piece into the forming die and press it by stomping on it or hitting it with a hammer. In this Instructable I'll show how to make the die and then lay out the shingles on a roof.
Making these can be tedious but the end result is gratifying because the old cans are fulfilling an immediate second life. A 24"x24" roof area will use from 36 to 50 cans (excluding drip edge and caps) depending on the vertical spacing and shingle style; that comes to 900-1250 cans per roof square (10'x10'.)
Start drinking now if you plan to try this.
I've recently posted how to build the whole coop at Diylife.com
Loads of uncrushed aluminum cans
Piece of 1x6 hardwood board
Two 1-foot 5/16" metal square rods
Circular Saw, or Router, or Saw with Dado Blade
Tin Snips or Scissors
Drill and bits