So my advice to them is to let me make a corner soap shelf out of the marble or porcelain tile that I and using in the shower. I can also make them like this out of porcelain tile but it needs to be a through body porcelain tile for me to make that happen.
I cut the shelf the way I want it shaped, then use a profile bullnose blade to create the rounded edge. Polish the edge to the desired finish and install.
here is a quick picture tutorial on how I make
and install a marble corner soap shelf.