Here is some FAQs I got off the SLO County Planning Department website.
Can I live in a travel trailer on my property?
San Luis Obispo County ordinances generally do not allow occupancy of a travel trailer on private property unless it is located in a mobile home park or, for limited time periods, in a recreational vehicle park. However, a travel trailer can be used while a home is under construction on the property, provided that permits for both the house and the temporary trailer are obtained.
What is the difference between a Secondary Dwelling Unit and a guest house?
Secondary dwelling units can have a kitchen and can be rented. A guest house cannot have a kitchen, laundry, garage, or separate electrical meter, nor be rented separately from the main house. Secondary dwelling units cannot exceed 1,200 square feet, while guest houses are limited to 600 square feet in size. A property is not allowed to have both a secondary dwelling unit and a guesthouse.
Do I Need a Construction Permit?
A construction permit is needed for almost any project that involves building or altering a structure or its plumbing, mechanical or electrical systems. Additionally, any project that includes grading, where soil will be removed and/or filled in, usually requires a permit. All of the procedures and regulations used to determine when a permit is necessary and also how to review that permit, are set forth in county ordinances and/or state law.
How large can a storage shed be before a building permit is required?
The maximum is 120 square feet with no utilities. You should consult with a Department planner to determine setback requirements and design review requirements. A structure larger than 120 feet, or one of any size that contains utilities, requires a building permit.