i'd like to build a lean-to type roof over my east-facing deck to provide a little shade & shelter over a doorway. i'm thinking 15' wide, 6' deep, roofing would be plywood - felt- shingles. bolted to house at high side, treated posts with beam(s) at low side. 2x6 rafters. what size end beam(s) should i use? we're zone 5, so maybe occasional 10" snowfall, and pretty strong winds any time. i just`need to know if this is do-ble. thank you.