3 x 6 is much too large for a shower floor, it doesn't offer enough traction. That's why you haven't seen it.

Try a mosaic or a small tile--2x2 squares, 1" hexagons, basketweaves, or the like. Any of them can be used for the shower floor with a large format wall tile.

It's not that you can't do it.

Generally, you need a shower pitch toward back wall and long linear drain near the same wall. A matte surface tile. And a LOOOONG chat with your contractor, pro tile installer, plumber, all.

Sounds like this may be above the skill set of all involved.

Linear drain is the ONLY way I would do it.

I think the big issue is your tiler does not know what an envelope cut is but those are the wrong choice for a shower floor unless you are doing a linear drain. Just get smaller tile same material same color and use mitcheing grout if this is a simple center drain shower.

Jan is correct, don't push installer to do something they may not understand. Revisit either tile selection or installer for the project.

Thank you all. I agree about my contractor and I'm going to talk to him again. I'm hoping it was misunderstanding on it, as he came recommended and has been around a long time. But with that, my current builder grade bathroom has 6x6 tile, why does that work and 3x6 doesn't?

Maybe you have been lucky : )?

The more exposed grout you will have with smaller floor tile will be added safety….soap or shampoo plus water can make a slippery shower floor with hard surfaces adding to the danger of a fall. Our master bath shower has 1”x1” floor tiles with sanded grout. The drain is round and centered in the shower floor. The wall tiles match the floor tiles in color, but are much larger. There is a triangular built-in shelf (about 15” high) covered in tile in one corner for putting shampoo and conditioner on, which is also good for shaving legs, if needed.

Don’t use 12x24 anywhere . It’s a dated / outdated trend . You are much better off doing subway tile on the walls and a hex or Penny tile on the floor