thanks mercurygirl, In the end, I've decided to go with the white marble corner shelves in the shower that were cut from the same slab as was used for the adjacent tub deck. With the marble, I can seal it (continuously :) and I was also a bit worried about the glass getting grotty too. They will be installed without brackets - the tile I'm using is Walker Zanger Tiberon, it's handmade and 1/2" thick, and the marble shelves will be installed with the tiles beneath it cut to accomodate the shape of the tile. The tiles that rest on top of that shelf will be whole tiles. It's a very classic, Beaux-Arts influenced tile design and I just love it. Of course I'll post photos when it is finished. My tile guys says that although the 1/2" tile helps a bit to support, he could do the same with a standard tile. Mortar is strong stuff!

If this is new construction, which because of your "home builder" comment, I'm guessing it is...then I doubt if it's a tile-over. Clamping drains are a threaded design, so the body can be raised or lowered as needed to get the correct elevation. Either someone didn't know what they were doing, or someone didn't know what they were doing. But they certainly knew how to fake it. You can certainly try to pull an explanation out of your builder. In general, the plumber is in charge of installing the drain and the shower pan membrane. The tiler is in charge of setting the drain height and building up the pan and tiling the pan. Sometimes continents collide and job paths get cross-contaminated. But in the end, your home builder is responsible for the action of his subs, however convoluted those cations may be. You can pursue this however you choose. I'm not normally one to recommend patch repairs. However, if you've had no negative issues with the floor; how it drains, how it dries? It might be best to leave things be. I say that with the exception of having to provide some form of proper support for the top drain grate. It might be best to remove the screws that hold the bottom grate, get longer screws, and install the top grate with the longer screws into the screw holes of the bottom grate. That'll secure the top grate to the drain body below. You can sleeve the screws between the two grates to provide support for the top grate with a 1/4" sleeve to fill the gap between the two grates. Perimeter support for the top grate can be added as needed.

I would miter the glass if it's on a degree less than 90°. In other words, if it's glass to glass and butting up at a 45° angle, then yes, I always miter my glass. A 90° angle, no, just butt up glass to glass, a miter isn't necessary and can look HORRIBLE if it's not glazed properly. Altho this question was apparently asked 4 years ago so this this response most likely isn't necessary either, lol. I stumbled upon this while looking for something else so I'll just leave it at that before I forget what I came here for in the first place. Other responses seemed to cover this just fine anyway.

"He coated the dry wall with the water resistant red material." Hopefully he did not use drywall but cement board as drywall with Redguard is a big no. Drywall has not been approved for this type application for years.