So having finished applying redwood slats to the ceiling perimeter, the next step is to do the same for the top of all four walls. Using those same 4 foot slats, it is a relatively simply matter of screwing them onto the galvanized metal frame. I say relatively because I am presented with two challenges. First, evey few feet the metal frame is attached to the aluminum ribs with pan head screws which protrude slightly. In order to avoid a wavy, irregular surface to which I apply the birch, it is necessary to rout a circular groove into the redwood where the screws poke out. A few pics will better explain this. Second, as I mentioned earlier, the galvanized metal perimeter it stout enough that it requires drilling before installing the screws, a step not required when affixing the slats to aluminum.