As far as what you can legally own in CA, be very sure of local laws before buying any AK. It could be a non-converted Saiga is the best option but I can't be sure as I don't live there.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek