Garden Room Re-Design. Soundproofing Design and Material

Description

Please see attached picture.
I have a garden room which I would like to fill in the walls, add window/door etc however I wish to use this room as a music room.
What I would like is a design both conceptual but MUST include detailed design on materials required to complete the project. This should include wall and ceiling construction etc.
It should look appealing and sit well in it's current position.
As you can see by the current design the roof effectively sits on 4 stilts. The size is 3.2m x 4m with a ridge of 3m
Not wishing to stipulate to much I suspect a block wall construction, clad etc might be best but am looking for good advice.Regards
Matt