I had to put in a header above the shelves (2 2x12 with plywood sandwiched in between). I knocked the drywall off and framed the shelves inside the garage so they would be flush with the wall inside. I then covered the insides of the shelf areas with sheets of beadboard. I used quarter round to support each shelf. I bought prepainted MDF shelves. I bought a door frame kit that was small enough for the spot and that I liked the look of. I cut them to size and nailed them in place. I finished by caulking and painting everything.