Recently I made a post in the WTB section for a flash adaptor for the Olympus XA4. The XA4 is a 35mm compact with f3.5 28mm lens, and it focuses as close as twelve inches. I didn't get a response, and I didn't really expect to. The camera iself is pretty rare, and the flash adaptor is even harder to come by. It is pictured and described here:

I think my chances of finding one are pretty slim. However, looking at the thing, it doesn't seem to be much more than a diffuser and a mirror on a hinge. How hard would it be build something like this? What would I need to consider?