Land Surveyor, maybe. Building permit, Yes.
You need to go through the proper permitting through the Ventura County Department of Building and Safety. Here's the link: http://www.ventura.org/rma/build_safe/information/index.htm
If you abide by the permitting process then you will be able to include the square footage in the total square footage of your home which will increase the value of your home.
Skipping the permitting process is not a good idea as you will not be able to add the square footage when you want to sell.
Also, the permitting process will trigger a property tax re-assessment so be prepared for that.
Web Reference: http://www.servingtemecula.com