Home Studio Soundproofing

I consider myself pretty adept at setting up music studios in the homes of my clients, but this latest challenge has my stumped. I have a guy who’s a rap stylist and he wants to completely soundproof his studio so he can teach other people how to make beats. I told him the general soundproofing gear and design should work, but he wants it industrial strength.

Any advice for me so I can help this guy out? Thanks in advance!