Thanks for the responses, especially dmun for the link. We're still considering possibilities, and this one has really caught our eye:
Monterey Masonry: Bake Oven Journal
I suppose there's no reason that kind of a base couldn't be built on the same sort of slab as the usual block wall. One might argue that as inexperienced (meaning zero experience) masons, we're insane to consider such a structure, and one might in fact be right.
In any case, it's interesting to see such different construction. It's kind of neat how the structural masonry and the finish are all one--no veneer.
-Ed