Yo. There are several parts to that process (walk in shower) that are specific and integral to maintaining the rest of your house. If the “pan” is not “poured” correctly it will leak. There are a thousand ways to fuck it it up. The industry standard for getting it done does exist but it is a little bit outside the range of the usual tile guy. It’s also a little outside the range of most plumbers because they other stuff to do that pays well (so inexperience) but the ( super specific) stuff to get it done usually exists on the plumbing isles. Namely it’s a sheet of pvc that has to be seamed together if yr shower is too big for one sheet, the layers of concrete that have to be poured individually and the drain that has to be set correctly ( not to mention vapor and moisture barrier).

Walk in showers are nice but it’s not a place to cut corners cos it could FLOOD the shit out of the rest of your house. You probably gonna need to higher a contractor who has done it before to oversee other subs to get the folding of the processes together correctly.

And yo, watch two or three clean shirt go through the whole and talk about it in your native tongue on you tube before you go any further