I still need to decide if I am going to put a small patio / slab / stone around it.

As long as the stone has some protection against the heat, any type should be fine.
- The concrete brick that lines the pit is the first piece of that.
- The core of the wall is 8" thick contruction block that is hollow, which provides a good thermal break between the inside and outside.
- The pit is big enough to have the fire biult in the center, not against the walls (which get them dirty anyway)

After a hot fire for about 4 hours, the outside wall was still cool to the touch, and the top stones were OK. I couldn't put my hand into the pit area for more than about 2 seconds, as it was very hot. This indicates to me the stone should last a very long time.