The step of building the house for your family at an incredible discount vs buying can work a lot of places. It's not very repeatable to do it commercially though. I DIY'd my entire house for extremely cheap but even in one of the most generous spots in the USA they only allow me to build a house once every 5 years and I have to file a sworn affidavit I do not intend to sell or profit off of it. If you want to do this as a business proposition as a random unlicensed person you'll be fronting all your own capital and then looking at about 5-6 year turnaround per time, and the buyer likely won't be able to use a mortgage, plus (in my case at least) I'd be subject to prosecution if it came to light I was doing that for a living. The smaller scale version of this is motorcycle/car curb-flippers that don't spend a gazillion dollars securing a dealership license, probably a bit more accessible but again as soon as the state or real dealerships get a sniff you're fucked.

I can recommend doing this to make a house for your own family but I think you have to be a bit insane to front your own money to build houses in almost anywhere in California as a business proposition unless you have a contracting license, which is to say, you already were able to make a decent living. I only got away with doing it for my family because all the people who could have brought the insane rules down upon me were kind enough to realize it was just a family trying to survive, they'd have fucked me with all sorts of inspections, shenanigans with the utility company, having trouble getting water, trades licensing, engineering stamps and plans, etc if they'd have gotten a sniff I had done this "again and again."

This kind of stuff did work fairly well up until in the 60s/70s before developers got in bed with the regulators/planning and zoning boards. Back then a guy and his truck could become a developer easily.