I understand that this is outside of your allowable square footage, but posting what I have that works. It is a 24x30 pole barn (720 sq. ft.), fully finished inside. It is double insulated with an insulating material called "Double Bubble". I purchased it with my pole barn kit from a place here locally called Kidd Fiberglass (
www.kiddfiberglass.com, 11741 US Hwy 431, Utica, KY, 42376, (270)733-4004). The insulation is like bubble wrap I use for shipping but different and is installed like Tyvek house wrap. It is a 3 layer (all in one) poly insulation that comes in a roll. The insulating material is about 1/4" thick. Between the outer layers (face side and back side, if I may call them so) and the center layer there are tons of tiny bubbles filled with air. A single layer gives you R-3. When I was building my pole barn, I applied a single layer of Double Bubble on the outside of the framework (between the outside of the structure and the metal). This application technique also provides the benefit of a vapor barrier for condensation, due to the outside of the building being metal (metal DOES sweat). When I started finishing out the inside, I framed it up like the inside of a house (16"-24" studs and trusses). Typically, pole barns are built with 4x4 and 4x6 posts and trusses set on 5 foot center (economical means to an end). I framed up between posts and trusses at 24" center, because I didn't need the added material for structural support just a way to anchor materials. I applied an additional layer of Double Bubble on the interior walls and the ceiling. This brought me up to R-6. The beauty of it all is: R-3 outside, R-3 inside and a 4" vapor barrier between the two (due to the width of the studs) gets me R-12 minimum and my building breathes. No sweat, no mold (at a fraction of the cost of fiberglass insulation). I have a floored attic, 30' L, 6' W, 4' H (to store stuff/parts), with pull down stairs. I finished out the inside with 7/16" OSB plywood, 200 Amp electrical panel, 15 KW mobile home heater, 60 gallon air compressor, tons of cabinets and counter space and (7) 8' florescent fixtures. I have space for all of my bikes, parts and etc., plus room to work on my vehicles, as needed. It fits my bill, Andy.