Speaking for myself, it helped a lot to have another pair of hands for much of it. I enlisted my dad a lot and my friends a little bit. Anything involving moving a whole sheet of plywood is tough, especially when going from ground level to attaching to the structure.

I did all the smaller stuff myself, including framing, putting together the roof trusses, and roofing (minus the sheathing itself). You can easily manhandle around dimensional lumber by yourself; it's long but skinny easily to easily handle, unlike sheets.

There are parts of framing that are safer and easier with 2 people, but there are a few places that I used a block and tackle to haul stuff around by myself. The only days that I really needed extra hands was setting up the posts & beams (most buildings now don't have these but I liked the idea), and setting the roof ridge beam, a 27' long pair of 2x8s that needed to be put 25' off the ground and 15' above the floor decking before any of the supporting structure was in place. Sheathing the roof would be smarter to do with 2 people but I didn't.