Historically, the original idea wasn't MAKE one, but FIND one, surely? - a recycled Peruvian packing crate.

I've thought about it - I could easily make one - but for now have decided not to go for it. They're not very portable, and I carry a lot of instruments around already. A Middle Eastern frame drum with jingles (like my Kurdish daf) provides a similar range of sounds, and it's flatter and lighter.

The good thing about the cajon is that it stimulates the player's imagination in ways that the bodhran doesn't. This is purely a historical/cultural phenomenon and in no way intrinsic to either instrument, but you don't find yourself thinking "oh no not again" when a cajon-shaped box comes into the room. Anybody who's got one probably knows something about Latin American, African, Indian or Middle Eastern rhythms - you can pretty well guarantee that a bodhran owner won't.