I built a 4-string resonator cigar-box guitar; quite nice actually. Keep it in open G mostly... I can sing in G.
I put a piezo pickup in it and the little guy can sound downright nasty played through an amp.
However, I wanted a full-sized resonator and had no money for such things... So I converted a cheap (very cheap) steel-string into a resonator.
Used the same principals as with the cigar-box guitar after seeing a video of one of these on YouTube.
Cut a big hole in the top, mounted an aluminum "warming oven" bottom into slots cut into the back braces... Cut a small hole in that and added a "bisquit" bridge and made a tailpiece and a cover out of old serving trays from Goodwill.
Got about 60 bucks into this puppy. Piezo mounted on the bottom of the bridge.... Actually sounds pretty decent!
Mostly doing delta-style blues with the thing.