Put a layer of plastic or roofing felt on the floor. This will prevent the flooring from absorbing water from the concrete and causing the concrete to dry too quickly. It also will provide extra water protection for the wood. On top of the plastic, put a layer of wire mesh. Staple it down. You now have the base for the concrete shower pan.
Install concrete backerboard on the lower half of the walls and over the threshold. Measure the distance from the center of the drain to the edge. Using the scale of 1/4 inch for each foot, calculate the height for the proper slope. If your distance is 4 feet, then measure up the wall 1inch (4/4) and mark the spot. With a level and a straight edge, extend the mark all the way around the shower wall.
Mix mortar for the base. The mixture should be 1 part Portland cement to 3 parts sand. Make it quite dry. Build a 2-inch wide screed of mortar around the edge up to your mark and be sure it's level. Make a ring of loose concrete around the opening for the drain, but keep it lower than the screed around the edge. Press the drain down and level it. Fill in the rest of the mortar and screed it smooth. Use a board to do this.
Waterproof the mortar bed as soon as you can walk on it, normally 24 hours. Apply thin set several inches around the seams and install 5-inch strips of the Schluter-KERDI membrane.
Seal the inside corners with the bottom of the backerboard and top of the preformed corners. Use the precut section of the Schluter-KERDI fabric for the shower floor. Apply a layer of thin set to the floor and set the membrane on top. Smooth into place.
Continue to apply the fabric to the walls until the entire surface area of the shower has a covering. Make sure you put cardboard down on the membrane when you do this to protect it. Allow this to dry overnight before you waterproof test it. If the area does not lose water, continue to the next step.
Apply a layer of thin set over the membrane and install the tiling. Use the Schluter-KERDI grate assembly when you install it.