Revised Idea for Garage...help!

I have revised my plans slightly. This is NOT to scale but close enough and I have listed what I believe would be the actual interior spaces left over after building walls. I still have no real idea of how to approach this. My friend who owns a construction company says he can quote me this week on building it. I am looking for any suggestions etc. that I can throw his way. I live in the country, and currently I jam in the untreated loft room above this garage with nobody complaining. I do not need crazy isolation, but want it to be good enough for project studio use and not hear a drum kit like crazy in my control room. Thoughts? Am I crazy? War :lol: