We had planned from the beginning to have solar and a rack on the roof. We decided to go with Unistrut. We applied a layer of eternabond tape to act as a barrier between the bare metal of the Unistrut and roof.
We bolted the Unistrut directly through the roof close to the metal beams. We used rubber washers and silicone on both sides then Dicor on the roof bolts to make sure everything is waterproof.
We bought 5/16 pine tongue and groove planks. We attached them using wood to metal self tapping screws. We cut the ends at a 45 to match them up.
In this picture and following pictures you can see we installed wood on the walls. We ended up removing it later after we started framing.