Apply mortar to the wooden floor in the shower, tapering from 1 inch thick at the walls to nothing at the shower drain. Cover the mortar with tar paper. This step is not necessary with a traditional install, but is needed on a plywood floor to provide slope to the shower liner to help it shed water properly.
Install the shower liner. Place it so that it runs up the side walls about 6 inches and wraps over the shower curb at the front of the shower. Do not fasten it as nailing it will create a hole that can potentially allow water penetration. This step is crucial as it is what makes the installation water tight and prevents the water from rotting the plywood floor. Without the liner, the shower couldn't be built on plywood.
Cut an X in the shower liner where it covers the shower drain pipe. Use PVC cement and glue the tabs created to the inner sides of the drain pipe so that any water that makes it to the liner will flow down the liner and into the drain pipe.
Pour the shower floor on top of the tar paper from the first step. Start at the walls with a thickness of 3 inches and taper it by 1/4 to 3/8 inch per foot until it reaches the shower drain.
Install the tile backer board on the shower walls by screwing it into the studs. Place a screw every 6 to 8 inches along the perimeter of the backer and every foot in the field. Extend the backer board over the shower pan liner on the walls and stop it about 3/4 inch from the top of the shower floor. Do not screw the backer board within 6 inches of the shower floor to avoid penetrating the shower liner where it runs up the wall.
Tile the shower floor and curb and let dry. Cover with rosin paper and plastic to protect the floor. Once dry tile the walls.
Grout the tile and apply a tile and grout sealant to the shower floor and walls once the grout is dry. Reapply the sealer twice, waiting 24 hours between each application.