With the rafters in place, it was time to clad the roof with some sort of solid decking, before the water/wind shield, and then the steel.
Both Grandpa and I agreed that it made good sense to use up my huge pile of 1x4 boards, rather than purchasing any new plywood or something of that nature. I believe this option is also encouraged by the CMHC construction handbook under environmentally friendly practices.
Grandpa was the first up the porch roof, balancing on the rafters while starting to place boards up the main roof. As much as Grandpa was set on using nails to work at this part of the project, I insisted on screws (thanks to a vague feeling they were "better" - as it turns out, there is much debate on this point in contractor forums. Most professional opinion running towards nails as being a better solution - but perhaps that's because they are much faster to install, and cheaper?).
We placed two screws at the end of each board, and then a single screw that alternated back and forth between the top and bottom edge of the rafters it was passing over.
I made the decision to overhang the boards about 16 inches at each end. This should protect my gable ends from the weather. This also worked well with my overall dimensions, as I am purchasing 15 feet of steel roofing. 12 feet of roof, plus 32 inches of overhang, leaves me still 2" of overhang in the steel. On the sauna I opted to forgo the trims to finish it off at the edges, and instead, simply overhang the steel a few inches to help it shed snow and water.
Eventually we worked up to a height that allowed us to more easily move inside the structure to put on the last few boards. Once we were in danger of getting our heads stuck, we switched to the opposite side of the roof and worked our way about halfway up.
Then we set up a stepstool inside on the loft, and completed our first side.
With that accomplished, it was back outside to dismantle one of my ladders and use the two sides of it as a bit of a makeshift scaffold. We dropped a long, rough cut 2x4 across the tops of the ladders and I screwed it to the deck temporarily with some 3" screws. This was enough purchase for us to complete the decking! It looked really great, and we were rather proud of ourselves.
By this point, I had dealt with my fear of heights enough to actually clambor up top to pretend to have a dogfight with the dreaded Red Baron!