That kind of thing is a lot of fun both for the builder and the spectators.
It's been a while since I've been to MidOhio Vintage Days, but some years back, for several years in succession, there was a guy there who would set up in the swap meet area with his van, which was was set up as a really nice little shop, with an awning out from the side that was the main work area, with a bench, vises, grinders, pillar drill, etc.
He'd generally have a few bikes and parts for sale, but his main thing was that he'd show up on Wednesday or so, and for the next 4 days would build up a bike from parts, sometimes from what looked like a pile of rusty junk. I can't even remember what kind of bikes; things like 175 MVs or Villiers-engined Brits or (once) a BMW 250 single. Sometimes he'd have to go find a vendor that had a part he was missing.
What an interesting way to meet people, and to concentrate your efforts on building a bike! I know I was always interested. .....
Lannis