I just framed a bathroom last summer. Basically for the walls I just used studs 16" on center, I used a fiberglass shower which gave the rough-in dimensions for the lower unit and the walls. I think I did need to add two additional 2 x4's to support the wall dimensions. I hired a plumber and he used my scrap 2 x4's to bracket the shower head and faucet assembly. I also added an extra 2 x4 as a blocker so I could install the vanity cabinet. It takes some thought--also I would mark the locations of the supply lines and drains and then put those markings on your drywall so you don't inadvertenly screw a drywall nail through one of your hidden pipes. Hope this helps.