can i convert a garage into a legal unit?

[Joseph Lee]

There is a property I am looking at. has 2 detached buildings. One of the buildings has a 3 car garage on the bottom, and a 2br +1 bath above it. The tenants do not use the garage. Is it possible to convert the 3 car garage into another unit( 2 bed +1 bath + kitchen etc.)?  about how much does this typically cost and would it add as much value as the other units?  I am assuming the garage is as large as the unit above it. (720 sq ft) The property is located in LA.