Greenhouse advice sought from SoCal, Southwestern folks

[Ray]

Another vote for height, but for a different set of reasons.

The lower the surface-to-volume ratio, the more stable the interior environment will be, year round. A cube is better than an elongated structure, but not as good as a geodesic dome.

With added height, you get significant differences in light levels, based upon the distance from the glazing, as the glazing is the "source" of the light, and inverse-square still holds true (although the size of the "light" is huge).

Concerning the slab, that really shouldn't be much of an issue. A decent carbide-tipped drill bit to make holes, and expanding anchor bolts to attach the base to the slab is really all you'll need.