Howdy, sounds like he did his best to make a nice tile floor. It is unusual to tile under a shower. The tile may interfer with the drain plumbing. The toilet flange of the drain pipe seems to work better when it is not flush with the flooring. But he might no have a leak if he uses the wax toilet ring with the plastic insert. Before he installs the shower you might have a tile installer come and give him some insights or a plumber.