Needing some guidelines for little guitar cab booth

Hello from Brazil! I am in the process of improving my project studio acoustics, and right now my main and biggest problem is guitar recording. I've finally found a sweet spot where the recorded tones are great, but my neighbours (and the other people who live in the house) are complaining a lot about how loud the guitar is. So, i've done some reasearch about Iso Boothes for guitar cabs (On my case, a 2x12), and i've found some info, but not anything very clear. My main questions are : Size - How large it should be, and what 'ratio' (WxLxH) it should be to sound good ? Treatment - I can get some rockwool to cover the inside walls of the booth. I can get 5cm deep and 50kg dense panels. Is that enough to avoid boxyness ? Would i need anything else than rockwool to treat the booth ? How much mass is enough for this purpose ? 3/4" plywood + rockwool ? Do I need a drywall for that ? Thanks for any help you can give me. Ivan