Have a piece of black marble the thickness of the lip cut to fit the bottom. Then fit it in place and caulk around it. Use a bit of shelf liner on top, the no-slide rubbery kind that's mostly holes, to keep things from falling out. Wash it every week.

A border could look look like a pasted-on afterthought compared to the nice edges the niche already has.

Jesus, that is horrible work. Makes me a bit nervous as to whether he bothered to waterproof anything. Doesn't seem like the brightest bulb. I'd ask him to brainstorm how to make it sloped so water rolls out and see what he says. Perhaps he's such a nothing that you don't want to deal with him at all, which I get.

A BORDER? No, please. The only "border" that should have been used, and was not? Schluter.

It's a totally lousy job all around. When you say "wish he had used a border" ......these are things you specify and discuss and put in a drawing and in writing. I'm glad for you he didn't, as it is busy enough as is.

Honestly, I SO wish the niche concept would simply die. The floor of the niche, should never have been tile. Even the tiled shelves were a bad idea. Grout is NOT waterproof. A solid surface is that, and it is why you do not tile bench tops, curbs, or the floor of a niche in a shower as all are horizontal plane and an invitation for leak with sitting water, even when pitched. It is easily avoided with a solid surface.

I am curious to see the shower in total..........

All of it to include curb, and anything else in there. What waterproofing system was used?

Tear it out and buy a prefab niche that is solid with flange.

So mnay things wrong with this. I really dislike niches ususally when there is a leak it is there . As Jan said all wrong. If fixed now it will require a rip out and a redo of the whole shower . Next time forget the niche who ever decided shampoo bottles were decor Get a nice caddy done. A border would just be lipstick applied badly on a pig.

Schluter was used behind everything.

It’s also a prefab niche from Menards

I know you said no redo, but I would seriously consider replacing the bottom and sides of the nixhe with your wall tile, so that the black tile is only an accent on the back of the niche. This would enable you to use solid pieces with no grout lines. It also makes it easy to slope the bottom towards the front. It's really not that hard to redo this, assuming they used some sort of liquid waterproofing that can be reapplied. The Schluter could also be fixed to face the front, but this would require using something to build the niche in, making it a bit smaller so that you can use Schluter to cover the exposed edge of the niche tile. Maybe find someone you trust to fix this? It should take less than a half day.

It was this product that was put in.

You paid for this and you are entitled to have it your way. Even if it means extra expense, you will be happier you had it corrected now then dealing with the cost of water damage later. It appears that section can be redone without destroying the entire shower. Perhaps you can have the surround tile be used as the shelf bottoms for a smooth surface, with no grout. There are solutions to every problem. Dont panic. P.S. I hate schluter. It looks like a cheap way to cover mistakes but it has its purpose.

Silicone a Nocturne (solid black) Corian stool with a pitch over the tile and forget about it please.

Looks like an edging was used - it was just turned so that the thick part is flat inside the niche - the thin part was faced out along the sides.

The niche should be waterproofed - if schluter used + prefab (assuming correct install install). I think adding a solid surface to the bottom of niche (Corian or quartz?) + pitched correctly would be the least invasive (as suggested by @Joseph Corlett, LLC above). Silicone the inside part of where the solid surface bottom shelf meets the back wall tile + pitch it correctly.

OR

Have it torn out and redone with the correct pitch (as it should have been originally). You have the right to expect that it was constructed correctly.

I just don’t know how you tear it out without compromising the waterproofing on the walls. I assume that it can be done using the correct Schluter products???

Your installer could actually then custom size (enlarge) the niche to line up with your tiles - based upon my research (a lot of time over on John Bridge Tile Forum) - installers with the most experience/qualifications build their own niches - they don’t use pre made ones.

You also could get rid of the thick divider - and instead use the same solid surface for your shelf + sides of niche (totally eliminating the need of using Schluter trim - I’m not a fan of it - except the way Beth H used it in her niche - looks really nice).

Here’s how this niche was installed.