Okay, I laid on all the roofing from the front of the shed to the rear, and when I got to the rearmost sheet the problem was plain as day; the SW pole was a couple of inches out of square. Everything else was okay. So I unfastened everything at that corner and cinched in the top of the pole with a rope until it was where I needed it, then I screwed everything down, cut off the excess, and fastened the roofing.
Good! Hopefully that was the hard part. Now tomorrow I’ll put up the wall panels and rodent-seal the whole shed except the front entrance with hardware cloth. Maybe I can finish that tomorrow. Then I need to scrounge about 40 square feet of relatively flat shale, haul in some sand, do the floor, and then I can finally get that big pile of firewood out of my yard.