I'm new to this too and another "victim" of the Sunset magazine article that my wife read.
Also in Southern California in a tract house but a larger back yard then most. Our lot is somewhere shy of a half an acre. Much of the back yard is taken up by our pool area but somehow we managed to set asside enough area for our coop and run.
8 chicks to start, 4 rhode island reds and 4 silver wyandottes. One RIR died. Now at about 7 weeks it's clear one of the SLWs is a roo, the rest appear to all be hens.
I perused this site quite a bit gathering data for our coop. As I've never framed or roofed anything before so I needed all the help I could get. I'm pretty sure the finished product would pass inspection for an atomic shelter, perhaps I over did it a bit.
We got as much of the materials as possible from our habitat for humanity store but still ended up at Lowes more times then desired and spent quite a bit more then expected for the whole thing. somewhere in the neighborhood of $800 when all was said and done for the materials, feed and chicken accessories.
Now we have an $800 chicken prison to protect $14 worth of chickens!
Anyway, here's my page with coop progress and pictures for what it's worth.
https://www.backyardchickens.com/web/viewblog.php?id=38201
BTW: Yours looks like a great start. Keep updating the pictures with the progress.