Step 1: prep the fireplace by spraying painting fresh black and clearing the wall. We kept the mantel in place as we had the mantel built thick enough to stand out through the stone.
Step 2: build a base. to do this we used rough cut 2x4s to bring the base a bit off the wall and give the stone depth. We then use plywood to cover the frame and to give the stone something study to hold on to (it would pull off the drywall).
Step 3: lay the stone out on the floor to make sure all pieces align and fit well. Work one by one and attach to wall using thinset.
Step 4: finished product