The pics below are from a neighbors house that did this. I REALLY like the way it looks, and frames the tree. I also like how the stones are at about ground level, so when you mow on the outside, you can go over the stones without sucking up mulch. I'm not sure what stone he used, and I'm not sure what size is better to go with. I stopped at Home Depo, and they have sone that is 12" long x 4" high, and then ones that are about 8" long, and 3" high. see pic. I want a tan color. I only want to do one layer in a circle. Advice? Pros? Cons?