Mud bases covered with a topical membrane are usually 1-1/4" thick at the drain and slope up 1/4" per foot to the wall. For a 4' square shower, that's about an extra 1/2". So figure 1-3/4" thick at the wall.

On top of that sloped mud you'll have the membrane, thinset and tile, roughly 3/8" total.

2-1/8" total. Add in a little extra for Murphy, figure 2-1/2" to be on the safe side.

If you do a CPE membrane that is set on top of a sloped mud bed with a second layer of mud over that, add 1" to the above number. That's being generous. It can certainly be thinner, but it shouldn't be thicker than that.

If you use a base like a Kohler cast iron shower receptor, it's about 2-1/4". For any of the tile-ready or preformed shower bases, you can look up their drawings online.

Typically, thinset is about 1/8" thick and tile 3/16" to 1/4" thick.

Your mileage may vary...

That's great information Mongo -- thank you! I have started to look at the preformed bases, but have been stunned by how expensive they are.

Do you have any suggestions for products that provide good results without breaking the bank?