Don't lay tile over plywood, which can swell with moisture and break the tile bond. If you're not pouring a new floor, mortar and screw ¼-inch backerboard over a level subfloor, then lay tile on top. Another option: Put in a DITRA flexible underlayment, which helps prevent cracks in ceramic and stone tile by evenly distributing the weight they carry.
Tear out the existing piping (Photos 5 and 6). Then frame the 2×6 walls that will contain the new plumbing and the opposite end of the shower base (Photos 8, 9 and 14). It’s easiest to nail the bottom plate to the floor and the top plate to the ceiling, then fill in the studs one at a time by toenailing them in at the top and bottom. Stack the studs directly in front of the old ones wherever possible. Space the studs in the center of the shower about 12 in. apart to leave room for the shower valve and showerhead. The studs behind the toilet should be spaced exactly 19-3/4 in. apart for securing this toilet chair carrier (Photos 8 and 15).
Interior bathroom demolition costs $1,000 to $2,300. Prices can go higher if you’re removing and moving walls to create a different footprint. For the experienced DIYer, this is a good place to save money by doing it yourself or assisting the contractor. However, demo can get expensive quickly if you take out a load bearing wall, cut electrical lines or break a water pipe. Avoid the risk by hiring a pro. 
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