Instead you can just secure the metal roof directly to the wooden beams cut the roofing felt to fit with a utility knife.
How to install metal roof for backyard patio.
Make a cutting on one of the sides of the horizontal roof beam on an angle.
You have to do it thoroughly so that the rafters sit flush on it.
How to install a patio roof using corrugated metal panels installing closure strips.
After that to make it flush with the roof of the existing house cut the two outer rafters.
To install the closure strips attach the strips to the top of the blocking with galvanized.
If you are installing a metal roof on a structure like a patio cover you may not need this insulation layer.
The roofing felt will lay horizontally along the plywood deck of the roof.
As for the corrugated metal roofing i chose rubber washer metal into wood screws with bolt heads and used a magnetized drill adapted socket to put them in.
Attach the horizontal beam by using a nail gun.
If you want to install steel over asphalt your best choice for installing metal roofing is to use a steel shingle system like the one shown instead of the more common and more expensive standing seam steel.
Lay the starter row of metal shingles at the drip edge and affix to the roof with metal roofing nails.
Most metal shingles will be attached to the roof using metal shingle.
Work up from the initial row starting at the lower corner in a diagonal pattern staggering the shingles to prevent gaps.