Hey builders! I need some random thoughts for the design of an unconventional stringed instrument.

I have this friend - to say that he's one-of-a-kind doesn't do it justice. Imagine a burly, tatooed biker dude with a nose ring... who loves kittens and guns and Bible study. And has plenty of other issues :-) Yeah, that's him.

Anyway, last night, he asked if I would help him design/build a unique instrument for his own enjoyment. He'd like 3 strings, round/rounded fretboard and he'd like to play it violin-style. He has thick, stubby fingers, so larger is probably better. And he want's to play it with a bow. Doesn't have to look, sound or act like anything ever made - or it could.

My first thoughts were something like a fretted erhu. Might be interesting.

Another design inspiration came from the Stash stainless steel bass.
I'm thinking diatonic frets just so it's simple to get good noises. He has no musical background or skill. Just interested in playing around.

My only personal criteria is that I have to be able to build it with available materials and tools. Not going crazy here. But I also want it to make reasonable noises and be something he can and will actually play with. Thoughts from anyone?

Thanks!