I managed to get a little more work done, after work, last night. I'm planning to use plywood for the walls of the shower and then cover them with a
waterproof membrane. In order to have the membrane come down right over the tile flange, I needed to either custom cut a nailer to go between the shower and the wall that the ply will bump up to or make some modifications to the ply to account for the flange. I decided the easier way to handle it was the former.
I took out some scrap wood, ripped it to the height of the flange and then set out to make my notch. Since I'm trying to conserve space, the back wall of the shower will not have any internal framing. I'm planning to use a sheet of 3/4" ply which will be secured to the bed frame, a nailer that will be attached to the roof ribs and another which will comprise a part of the wire chase by the windows. Since the opposite wall will have its own framing (to accommodate the shower plumbing), I will be using some 15/32" ply for the walls.
All of this is just to say that I like to make things more complicated for myself. Using the same material for both walls would have saved me a little bit of time when making those nailers, but it would have lost me a little bit of space in the build. Either way, I've made my choice and now the shower pan is rough framed in. Next up I'll start to figure out the framing for the walls and try to start getting our cabinetry built. I'll also have to pick up some plywood to finish the bed area.