To install a gabled aluminum patio roof, get rid of old shingles, nails and dirt that might be on the roof structure, and cover it with some felt paper. Attach one section of aluminum roofing to the roof structure using wood screws. Make sure that 1 inch of the section is extending down from the edge of the roof. Place all the other sections on the roof one by one. Each section should overlap the previous one by 1 inch.
Climb onto the roof structure, and measure it before starting the roof installation. If you need to use a ladder to climb the roof, have someone hold the ladder so that it doesn't fall or shift. Divide the width of the roof structure by 16 inches, the standard size for aluminum roofing panels, to find the number of aluminum sections you are going to need for the roof. It might be a good idea to get a few extra sheets in case you damage some during the installation.
When covering the roof structure with felt paper, place the roll of paper at the peak of the roof, unroll it on one side, and cut the paper off at the edge of the roof. Overlap the first layer of paper by about 6 inches at the peak of the roof, unroll the paper to cover the second side of the roof, and cut it off again.