Garage Conversion w/o Permits

[Rob B.]

Can anyone tell me how big of a deal it is to have work done without permits? The work being the addition of a second bathroom to a 3/1 in San Leandro, CA and the conversion of the remaining garage space into a studio apartment with separate entrance. 

My long term objective for the property (currently my primary residence) is to live in it for another 12-18 months, then rent it out for 2.5 years (hopefully both sides separately) and then sell it. As an agent, I've seen plenty of houses listed that had work without permits done, so I don't know how big of a thing it is. Also, how much more difficult/expensive is it to get permits?