A very common option in California is a garage conversion. It generally has the lowest cost to build and is usually completed in the shortest amount of time. It is possible to have a garage conversion and add on additional square footage. In California, you can convert an attached garage or a detached garage. One big benefit of a garage conversion, is that you are not required to add a parking space this new area. The other big benefit is that solar panels are not required on garage conversions. For the homeowner that chooses to not add on square footage, and only convert their existing garage to a JADU, you will generally see a one bedroom, or studio style unit. The average two car garage is approximately 400 square feet.