The niche was put between studs and the window header in the framing (therefore non-structural), rounded corners, and tile continued on the lower shelf. The actual shelves are store bought pieces. If doing this yourself, get the shelves first so that you can build the niche to fit them properly.

We built this project. I think that the shelf came from COOLLINESUSA dot com. It doesn't look like they make the same exact unit anymore thought. - rf