garage lean to

I am looking to build a garage lean to on the side of my garage. I prefer using wood as the material for construction but I'm open to metal. The length will be 28' and the height at the garage will be 10'. I'm flexible on the width based on material and design constraints but I'd like to make it at least 15' wide (max width 20'). Planning on using metal/polycarbonate on the roof and metal on the sides. Attached is a rough idea of what I'm looking for framing wise