Good Dr. Hashman and BeFree, I appreciate y'all's responses.

Dr. Hashman, my biggest threat in the attic will be temps. I was delaying any indoor plans for a long time because I didn't have any idea of how to deal with the temperature issue. My family member is the one who pointed out he could pull another duct line to the box, so with that issue solved I think this box should fall into place pretty well.

I would appreciate further input from you when you have time upon completion of your own box. First hand experience really provides better insight. I have very little experience in construction, but have gotten some ideas from this board - I can use all of the insight and ideas people can throw at me. Thanks!

BeFree - dude, I would appreciate any drawing that you feel like sharing. I seriously thank you for the offer and look forward to checking out your thoughts! Thanks again for your input and great share!