shop roof: sheathing or purlins?

I'm doing site prep now for the concrete slab and barntype wood/mechanic shop...Shops at ground level, and loft will be craft room, intertainment and grand-kids area. Using gambrel style metal roof, do I need to use sheathing (OSB, plywood) or can I just run the purlins across the rafters, and attach metal ? It'll be insulated as well, so I guess my fear is condensation...sweat and such. Here in Nashville area we get seasonal weather not too extreme either direction. And I'ld like not to pay the current premium prices if I don't really need the material. Four hurricanes have greatly jacked up wood and metal prices. Any suggestions are greatly appreciated. Until then, I'll be playin in the dirt!!!
roy

Purlins should be fine. If you're worried about condensation, consider having someone spray on polyurethane insulation inside the roof.

roypat2126, When you do your roof may I suggest a ridge vent across the top or cupola's to let the hot air out [img]/forums/images/icons/cool.gif[/img] .
Mine is not insulated up top but with the ridge vents and soffit vents I have not noticed any sweating, But mine is not heated either.
Maybe you could put up sheathing or sheet rock up on the trusses that box out the room and lay your insulation on top of that. That is if your using attic type trusses.I don't think I would recommend putting fiberglass batting in contact with the underside of the metal roofing,maybe styrofoam would be ok, Oh and yes purlins will be fine also metal roofing only requires trusses every 4' , Have fun [img]/forums/images/icons/wink.gif[/img] Have added picture to encourage you

Much obliged AndyF, I'll check out prices on that stuff. I've seen it on TV, but always thought it might be too pricey... Thanks for the tip. on purlins. It'll save me a bundle on this bldg not using sheathing.
Thanks for your reply as well, Carb454.Now that's what I'm talkin bout ...That's a mighty fine lookin barn, ye got dare ! I'm hopin mine will follow suit, lookin like that in a few weeks. Looks like your trusses have knee walls like mine. Iwill be using gable vents and maybe a cupola for looks, and drywall up there as well and will use those foam baffles on insulation layer giving air path down to soffits. Playin in the dirt this weekend, gettin the site flat, grass free, ready for concrete pour. I'm excited about having a place to create a little sawdust. Soon as I get a picture I'll post it here where I can add to it as It takes shape.
Thanks again guys,
Have a blessed weekend,
roy