I would say exactly what you said: "I would like sills and jambs for the shower entry made out of [marble] matching the vanity. In addition I would like a casing to frame the opening, like the wood casing around a door opening, only made out of matching stone."

Don't just explain over the phone ... these days you can text or email your mockup photos too!

How do you plan to detail the "casing"? Those pieces will protrude significantly beyond the adjacent wall surface, especially if your slabs are 3 cm.

Dragonfly has it right - a written spec, with pictures, and everybody signs the document ahead of time.

This would be an in person discussion followed with an email and photos. The picture looks like it may be milled down to 3/4" and there is a horizontal seam on the top and the bottom between the upright pieces and the horizontal pieces. Make sure that the size is all figured out and that all finished edges are noted.

Looks great! Good luck

I like the way you’ve designed your shower - I think using the same stone (or whatever your counter material will be) as a frame around the entry of your shower will look really nice. I have an unusual partial wall that divides my shower from the area where my free standing tub will be installed. I found your post because I was trying to see what people think about using the countertop material for not only the top of the curb, inside the niche, and sill of pony wall - but also vertically up the edge of pony wall + the “jamb” of the shower door (my shower doesn’t have an opening like yours - so, I’m not sure if it’s still called a jamb if it’s just where the tile ends on the wall in line with the curb). I just don’t know what the correct terminology is for those other areas in order to look up examples where it’s been finished that way.