I did use a nail gun for roofing. I can't tell you how many partial to full cases of nails I have bought at yard sales for $5. A framing nail gun would have been a lot quicker, but I didn't have access to one at the time.

The walls I used the 6'6" 2x4s with one bottom plate and 2 top plates. This made the interior ceiling 81" tall. I started the siding at the bottom of the floor joists and ran the entire height to the top plate. This really solidified the structure. It left about 6-8" over the top plate that I cut off with a chainsaw. Next time I will cut it before I put it up. I screwed a 2x4 to the bottom of the floor joist to create a lip to set the siding on to hold it and screw it in by myself.

I am using the scrap siding to do the soffit. I'm going to pick up a few gable vents today to put in.

With the loft, I think this would make a great little off grid hunting cabin. A solar panel with battery for light and power, gutters to redirect the water into a more "useful" area. A small wood burning or propane stove for cooking and heating.