you can go to a city of Chicago neighborhood office for help with a project of this size. They can tell you what permits you need and how much they cost. If you have a single family home to as much as a 6 flat, you can be your own general contractor. But you must make sure any contractor you hire has insurance.
600 sqft for frame
800 sqft for brick or fire rated assembly
Must meet all set back and lot size requirements
If your garage builder doesn't know these, he isn't a garage builder. All info is available on the City's website. Garage permit runs a few hundred dollars. Must have GC and electrical licenses.