"...which are the most build-worthy?"
I suppose that depends - what kind of music do you play? What effects do you want/need to achieve your musical goals?
I love classic rock and thus I've built at least two dozen or more overdrives and distortions. It's very hard to name the best ones, but if you're looking for a good, versatile and easy to build overdrive, I'd start with the Clark Gainster. Eventually you will want to build a klon, muff, tubescreamer, crunch box, or one of the zillion variants. Have fun!