Your plumber is not the one who waterproofs the wet room- your tile person is. Once you figure out the layout of the wet room, meaning where the tub is going and where the shower area is, he runs his rough plumb lines as normal stubbing out the same way he would for a tile shower pan. Hopefully he has done a free standing tub before. They can be tricky since brands vary as to how they rough in. The big trick in roughing the tub in is it has to be spot on for the location since there will be no play after it is tiled. Once the rough plumbing is done, your tile person comes in and preps the space. We use Wedi products for the wet room walls and floor. Again not all tile people are familiar with this product or how to do this so I strongly suggest you seek out a pro. These spaces can be very cool, but they require fore thought and experienced tradespeople to pull it off.
Q
wall cubbies
Q