#1
SO.

Me and three band mates are making a studio/practice room/party room at our drummers house in his barn, the barn is big but the room plan is about 13ft x 8ft and 9ft high. We are making stud walls to make the room out of. So the question is how would we avoid bad acoustics whilst keeping ourselves and equipment warm and dry and keeping the room rat proof
#2
All those requirements fall in to one solution: Good walls. Make sure the walls are installed well and there are no holes, especially near the floor. If you insulate the room for heat, sound won't get out either. You could buy some soundproofing, or just get some really dark, heavy curtains and hang them an inch off each wall. Carpet the floor (I like shag, personally), and get a really good, thick door. I'd throw a space heater in there, too, just in case you want some extra warmth.
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#3
I suggest reading over Tweaks Guide in my sig and also look over their message board for room layout ideas and acoustic treatment ideas.

prepare to spend a lot of cash and work on a ton of tech. designs