in most regions, you will need a permit and a drawing of what you are doing and every phase of the work outlined for review. My region requires a permit and then you are increasing your living space which will increase your tax rolls and this becomes more than an addition quickly.
You then have HVAC issues, will the existing system take on the additional load and not let down the main home in Conditioning.
Is this garage detached or attached to the main structure home? This has allot to do with the project.
After considering these issues come back and we will take you to the next rung of the ladder.