More Shelter-Kit Houses

Build My Own House?

Lately I've been obsessed with the idea of building my own house, mostly because I live in the San Francisco Bay Area and housing is way too expensive. Not that building your own house is necessarily more affordable, but...
In a very roundabout way, I came across this company called Shelter-Kit that offers all kinds of kits for building your own home. Some are kinda modernist cool, others are more old-timey cosy, and all seemed to be pretty customizable.
Basically, you design what you want based on different modular units and materials offered, the company makes everything needed (including a super comprehensive instruction booklet), everything is shipped to your site, and you build the house on a foundation you have prepared beforehand. You have to do the interior finishing, plumbing, and electrical, etc. yourself, though.
Anyway, I'm just into the idea of having a lot of control over what's going into my house (as in "no toxic weird stuff") and being able to partially design it myself. Like I could add alpine chalet details, windowboxes, porch, whatever to make it look cool.
So, can I find affordable buildable land lots in the Bay Area? That would be the ultimate challenge to making this little idea a reality.