band practice in garage

[chas]

Hi,  I am planning on soundproofing the walls of the garage for band practice.  Here is what I am planning on doing, could anyone let me know if this sounds like it may work, or if I am wasting time/money on certain items.  Other suggestions would be appreciated
1. install 3/4" rmat foamboard (home depot) between old studs
2. install new studs between old studs that do not touch outer wall
3. install rolled roofing material over new studs
4. install 5/8" drywall to new studs
5. tape all joints
Then I will have to look at floor and ceiling options
Thanks