<snip> I also found that county building depts. have no lawful jurisdiction over private property, only over municipal property. Licensed building contractors have to comply with local and state codes, but an owner/builder is not under any restrictions. <snip>
What you think you found out is just plain false. In California, building permits are required for virtually any structure, whether built by an owner / builder or a contractor. In every county I know of, the Planning and Building Department is in charge of permitting, and their rules apply whether you are an owner / builder or a contractor.
There are exemptions for some structures: No permit is required for buildings on one to ten acre parcels of less than 600 square feet and 15 feet in height. No permit is required for structures on parcels larger than 10 acres, with no maximum square footage restrictions, but with a height limit of 25 feet. No electrical or utility hookups allowed. There are also some exemptions for agricultural structures, but you can't claim a workshop or garage is an agricultural structure.
Building permits are only issued to California licensed contractors or an owner-builder.
It would be foolish to think that everyone gets a permit. In my neighborhood in a county adjacent to Lake County, there are many structures that have been built without permits, but here is what happened to a friend:
'Joe' wanted to build a workshop building to house his machine tools. He chose to build a pole barn and since it was on 300 acres well off the main roads, chose to not get a permit. He built the structure and used it for nearly 20 years. Power was provided by a generator, so there was no reason to get a power connection (that would have required a building permit prior to hookup by PG&E).
After ~20 years, Joe wanted to move closer to civilization, and sold the property. The new owner applied for a permit to build a new house. At the first site inspection, the county building inspector noticed the pole barn, and checked his records: No permit had been issued. The County then demanded that the new owner get a permit for the pole barn prior to allowing construction to start on his new house.
That meant paying a fee and fine, then getting the pole barn inspected. Shouldn't be a problem, except that Joe, the original owner / builder had used untreated poles in the construction, along with some construction techniques that didn't come up to code. The poles were rotted at the ground level to the point that they could not pass inspection, and rebuilding the structure to meet current codes was going to be somewhere between expensive and impossible.
Bottom line was a lawsuit between buyer and seller, with lots of legal fees. No winner in any way.
I've got another story where it took us 4 months and cost $600 to get a permit for an outhouse at our local airport.
Bottom line is that you might get away with not getting a permit, but you might be real sorry in the future. I do not know of a single county in California that does not require a permit for a permanent structure.