Ah, thanks for the input. I was concerned about it because when I lived in SoCal, we cut down a small fig tree and a few years later, we ended up with a noticeable sinkhole where the roots had been. Unless that was just coincidence.
From what I've seen of the roots of these trees, they seem to be fairly small, but widespread. We're thinking of doing a slab foundation, rather than a raised foundation, and I was concerned that it might end up breaking from subsidence. There must be a LOT of roots, tho, because the trees (there are two more, farther away from the house) are just huge! And we'd be building very close to the base of the cut tree, probably less than 6 feet. (Can't get accurate measurements yet, because the remains of the tree are still scattered over the yard....grrrrr!)