Found a local builder and I'm going with a pair of 10x12s, with 8' interior wall height and gable-style roofs (about 11' to the peak). Although the gambrel would provide more loft space, I felt it looked a bit out of place in urban San Diego and I had to consider my neighbors with such a tall roof (even though the city allows more height). After some thought, I've decided on a simple block foundation, but with an extra skid and a thicker floor for rigidity. This will allow me to move them around if we ever needed to - plus access for slab equipment is very difficult in our yard and it's expensive!
This will be the general style - going to pony up for the paned doors and grid-style windows to make it look more house-style and repurposeable in future (office etc):
