Hi, and welcome to the forum!!

My advice would be to contact pool installers in your area to see how they deal with the shale, since ultimately that's who you're going to have to deal with. If you decide to go with above-ground, you're going to need a place that is level. I know next to nothing about the construction aspects, but maybe some of the others can come by and offer more useable info. Just wanted to welcome you to the group.......