Rich, I used to assemble drums quite often, using parts from the various suppliers (including some who are no longer in business). I wasn't aware that the suppliers today were offering single-ply shells...wonder where they're getting them from? Perhaps Keller or Vaughncraft?
You are correct that making your own drums (or having them made) can easily exceed the cost of factory-produced drums. My view on it has always been that custom-making drums is the best alternative when you know what you want but it's not offered by the "big guys." Maybe you want something that's different, or you're trying to achieve a specific sound, or as Ludwig-dude mentioned if you can't find a piece or need to repair/replace a damaged drum it's sometimes easier to try to recreate it using modern shells with vintage hardware. With a few tools and some basic woodworking skills all it takes is time and practice to become at least moderately proficient.
As for myself I've assembled drums for all those reasons, and also because once I "got the hang of it" I found I actually enjoyed it. I've done too many drums/sets to show them all but I've attached some of my favorites from the past...also, some of my postings in the gallery are my own creations (Slingerland mahogany set, Stanbridge snare).
Jeff