Welcome, Poly,
Hard to tell what material was used for that niche from the photo, but I'm confident it isn't marble - it is too uniform in color. Nor would you want marble, IMO; marble in a wet area, especially a niche where wet bottles will be stored, will be a maintenance nightmare.
Any solid surface fabricator should have an engineered product, like Corian, available, in different thicknesses. They might even have some leftover pieces from a previous job that they can cut up for you.
Yes, you do want grout lines; you do not want those pieces to butt against each other. I would think the inside edges should have a slight bevel on them, while the outside edges, where the tile abuts, can be square if you want the face of the tile to be in the same plane as the face of the niche.
I recently did a niche using some solid surface material I found at Lowes. While it isn't as white as the surrounding tile it was close enough for me. The material I used has both edges beveled so I installed it with the face proud of the surrounding tile by about 1/8" and grouted the joints.
__________________
Dan
---------------------------------------------------------------------------------
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
|