Installing a wet room is a job for the professionals, as a gradient needs to be created along the floor to channel the shower water into a drain and then the entire room needs to be tanked (waterproofed).
The most common method for creating a gradient is to install a sub-floor made from WBP Ply (a type of plywood), which is then tiled over.
Another option is to install a ready-made sloping shower former (a bit like a giant shower tray), which is also then tiled over.
A final method is to use a bespoke floor in the non-porous material HI-MACS that slopes towards a drain, and can be fitted across the entire floor without the need for tiling over.
Waterproofing wet rooms involves priming the floor, the lower section of the walls and the whole of the wall area around the shower and then covering with a syrupy membrane. Once it’s set, the room is then tiled.
It’s also worth raising the bathroom door threshold by about 5mm from the floor in case the room fills with water (if someone covers the shower drain with a towel, for example). This will keep the water contained.