[tharbert]

Well, at least you know the problem was basically because of a botched installation. The structure looks fine.

Those cement boards make easy work of reinstalling waterproof walls. I'd go with a neo angle base shower unit along with large stone tile (18x18, maybe) and a deluge shower head.

I would look for glass walls, not the anodized metal with Plexiglas. If the house is a keeper, that's money well spent.

If the valve hardware is dated or corroded, nows the time to re-plumb that valve.

Heck, you're almost done!