I love the look of marble, the same with most natural stones.

The problem is that yesteryear's marble was fairly consistent. If the stone was a lousy stone, it did not make it to market. Or it was re-purposed into another type of product. Today, with the advent of an open global economy, the ability to buy over the internet, and with improvements in not just mining stone, but also in technology (like resinating slabs) that allow manufacturers to recapture and bring stone to market that would have been rejected years ago...it's tough unless you know where your stone has been sourced from. Resining a slab can be a good thing in terms of slab strength, porosity, etc. But it also has consequences.

High-iron marble used to never make it into the residential tile world. It's all over the place now. Same with softer grades of marble, I've been given boxes of marble mosaic where finger pressure on the corner of the pieces can cause it to crumble.

If you want to use marble in a shower floor, go for a low-iron marble. Marble is porous and will absorb moisture, and that wetting and drying can cause iron deposits in the marble to oxidize, or "rust". You can end up an overall yellowing of the stone, or with more specific rust-colored stains or veining in your stone.

I also recommend installing the marble over a topical membrane. Hydroban, Kerdi, RedGard, etc. That prevents deep-wetting of the shower floor and helps promote drying of the marble.

When you create the slope, makes sure it is consistent. Sometimes the slope tends to flatten near the walls, then the wall-floor intersection is slow to drain or it can hold water.

When you grout, don't over-tool the grout. You want the grout to be flush with the surface of the stone, you don't want mini-valleys between the tile that can hold water.

So, 1) pick a good stone, and 2) control the water.

Easy-peasey!

i would want to make sure i had a shower floor that i could scrub, so i would check about that with whatever product i chose before it was installed! (i would rec a cast iron shower pan, myself!! :)

We have had a basket-weave marble shower floor for 2.5 years now with no problems. Floor is not slippery and has not been stained by liquid soap, shampoo etc. Grout coloration is a different issue. I am afraid to use bleach on the light grey grout lines to remove pink algae. So far, scrubbing with a towel, a steam cleaner or the occasional use of the magic eraser have taken care of that. Since the shower is a replacement for the bidet that was on that spot before and the rest of the bathroom already was tiled in marble 20 years ago the use of marble in the shower was always our only way to go. So far, no regrets.