we just went through this ourselves,we also are building our own house. there are many ways of doing this ,I found an article in a magisine that helped .first- two layers of drywall has the same insulating effect as fiberglass sound barriers,this will not completely sound proof but it will deaden noise to the point where you would not be able to hear voices but muffuled sounds.however if you do both (sound batts and drywall or drywall) you can barely hear any noise at all.If you want acustical sound that takes alittle more effort. Checkout "Homeowners" magisines back issuses thats where I read this article. If you do use double sheets of drywall on outside corners regular cornerbead will not work, we trimed it out with wood. good luck.