Step 1: Measure the Width (Projection)
Place your tape measure on the right side and against the house wall, measure straight out to a point where you would like the patio cover to end.
Repeat for the left side.
Step 2: Measure the Length
Place your tape measure at the approximate location where you would like your patio cover to start.
Measure to a point where you would like the patio cover to end.
You won't have to add for any overhang.