Hello, New state rules allow  California homeowners  an easier time building small second dwellings, (granny flats, accessory dwelling unit) on their properties.  

Applicable fees: assuming you are zoning compliant, building and zoning permit (Accessory Building, Fence, Landscaping, etc.), Parking Lot Lighting, and Thorough fare Fees at a minimum. pages 14, 16, 23 of the Raleigh fee schedule Expect $400 or more per space in fees alone plus attorney costs ($273/space Thorough fare Fees alone)Or... run covertly. 

Sometimes, Additional or accessory  Dwelling Units are allowed but local owner must still occupy the residence.

They do offer padlocks but I have never had to use them:https://www.kwikset.com/products/details/accessori...They offer both handsets and deadbolts.

Accessory Dwelling units are allowed if you intend to live in the home.   

I'd configure it as a 1 bedroom with an open floor plan to allow for a spacious-feeling office area.My wife and I are considering buying into a situation like that in upstate New York or Connecticut- we like the idea of an accessory dwelling unit where we could go to conduct business(she's in interior design, I'm in real estate primarily.)

UPDATE: After doing some more research there is something called an ADU (Accessory Dwelling Unit) that should allow us to do this 2 unit strategy. 

Thanks, StephanieAccording to one of the local Homestyle lenders, an accessory dwelling unit aka ADU aka guest house does NOT qualify as a one unit dwelling if the home is an investment property.

Hud or some other program will pay the rents for those who just want to hang out and Vape weed and play video games. for those nice neighborhoods not so much.

Also you probably want to work with an architect who has ADU experience I can recommend one if you want.Here is a recent article with more information: http://www.sfexaminer.com/city-easing-onerous-approval-process-accessory-dwelling-units/