Can you build an ADU/tiny home on piece of Land in Bay Area, CA?

[Kevin G.]

I'm a first time investor here and exploring many options on how I can best start out. One of the options I've explored was buying a small piece of land in the Bay Area and building a small home or ADU to rent out. I'm wondering if you're allowed to build an ADU on empty land or do you HAVE to already have a home on that property?

Thank you for any help.