ClownShoe ClownShoe is offline

For the most part it's a semi-auto shotgun and falls under those rules. You also need to keep it 922r compliant if you make it tacti-cool.

Peach State Guns sells CA-compliant Saigas right off the shelf:
CALIFORNIA SAIGA 12ga CONVERTED

That is your easiest route without spending a lot of time figuring out what is legal or not. You can hang out on calguns.com and read up on everything too.