I've had the thought for a "Home Depot" build-off for a while, but I don't want to get caught up administering such a thing.
The rules would be rather difficult to specify. The spirit of the thing would be no "luthier" woods, but the letter of it would be rather tricky to define. Perhaps it would be best to have a committee judge it on a case-by-case basis.
I could envision at least two classes:
1. "Home Depot" body, bought neck, since not everyone can build a neck.
2. "Home Depot" everything.
I would allow "luthiery" fretboards, as not everyone has access to suitable stock for that. But extra points for "Home Depot" fretboard. Even more points for not using wood at all. I wonder what kind of fretboard you could make out of Corian?
By "Home Depot", I mean any hardware store, hobby shop, or regular lumberyard. The idea is that the materials must be general-purpose, and never specifically intended for a guitar. Online wood sellers are ok, as long as the wood is not specifically for luthiery.
So if you have an ash tree and you cut it down and make a body blank, that would be fine, but buying a guitar body blank would not. If you buy a bunch of pieces of ask and assemble them yourself, that would be fine, provided that was not what they were made for in the first place.
Likewise, buying a mahogany neck blank would not be kosher, but making one from an old mantlepiece would be fine. As you can see, it is tricky to define.
Extra points for scrap, salvage and dumpster wood. If you can build it for free, so much the better.
Also, no gag guitars. The object is to build something you would take on stage, attractive and fully functional. So unless you can make a really nice job of it, no toilet seats.
As far as non-woody hardware goes, whatever you want. I wouldn't expect people to wind their own pickups, etc.
Design can be original, or a copy of a classic, or anything in between. Build a Rickenbacker out of deck boards. Any kind of instrument, build a ukulele if you want to. That would make it even more interesting.
Some suggestions:
Suitable neck woods include: maple, poplar, walnut, yellow pine, oak, and plywood ( yes, you can make a neck out of plywood. Why not? ) At least one of those should be available anywhere.
Suitable fretboard woods include: maple, oak, walnut, and hickory.
Suitable body materials/constructions include: there are too many ways to list.