Well after thinking about this some more, and doing some Net searches, I am becoming very fond of the idea of building a small (e.g. 10 x 10 interior) smithy of cob, with a metal roof. We have some pretty serious clay soil, so most of the material will be the cost of my sweat, plus some sand, straw and horse manure. I'm thinking a floor of crushed granite, abundant here in southern Oregon. Nice thing about cob is that it tends to keep spaces cool in summer and warm in winter. And if it ends up looking sort of like a shapeless blob, that's cool too, as most of the things I forge tend to be shapeless blobs ...
B)