How to build a custom shower tray from scratch or am i crazy

[Jeeves]

Hello, im planning on updating the bathroom for the parents this week.We currently have a very small shower tray, and i want to make the most of the space available in the bathroom. So im planning on building a partition wall so when in the shower three sides will be tiled (already two sides are)Just wondering if anybody has ever built their own base for a shower.
I was planning on using thick wood to bring up the height of the base to allow for the drainage point (although i would like to keep it as low as possible), and then using layers of marine ply to cover surface of the tray il be making.Then tiling it. I would be grateful for any tips as in what sealants to use, (or if i should abandon this idea.) cheers

[thedoctor]

See our projects section and look at the project wet room or walk in shower

[marrtin]

I don't think you will get a watertight seal with tiles. Wet rooms have to have specially prepared, cut and fixed materials.

Why do you want to build a shower tray anyway? They are available in a wide range of sizes and are you sure you can find a shower screen to fit?