I built a 40x60x14 this summer with help from family and friend and your supplier will have the insulation you need. It is only about 1" thick in 4' rolls, tack it to the purlins plastic side down just before you apply your roof siding, the weight in minimal, your condensation problem is solved, and and it is alot quieter when it rains. I went with a kit, and stepped up to the upgraded kit which got me the insulated roof 1' eaves on all 4 sides and soffits for $900 more. So based on that I'd say that insulation is pretty cheap. My 2x6 trusses are 4' on center, the purlins are layed flat 2' on center. Now my farmer buddy down the road has a 40'x48x16 , pole barn/ garage with 2x6 trusses 8' on center with the purlins on edge (like your talking about) with the same type of insulation under the metal roof. He has had no problems at all, in SE Michigan, In fact he told me everytime he helped me build that I wasted my money going 4' on center with the trusses but, my kit barn went up really well. One thing I would recommend since you are in the planning stage is to raise that barn site alot. I know so many people (horses) with wet barns because they built and then then tried to fill or solve their water drainage problems. So the first thing I did was bring in enough fill to raise my barn site 2', good luck with your barn [img]/forums/images/icons/laugh.gif[/img]