G'day John, 1st I thought hobs were out. You can use bricks for hob & then waterproof everything - primer+ fibreglass matting & then 2 good coats , do both walls of shower up to 1.8mts , the rest of the walls only has to be about 100 mm up as after that the water is running out the door . Next you lay the bed & make it slope to the waste. You put the waste grate in last ,it should just float, not actually attached, theory being if it does leak the water will run under the grate. Ihope this helps you. I'm sure somebody will know the rest of the answers.
Good luck.
Planepig