Shop Addition/Lean To design questions

[golfnut]

I currently have a 70x80x19 wood frame shop with a 5/12 roof. I'm making plans to add a 92x26 lean to on the south side that will house an office, 2 car garage, and some cold storage. My office/entertainment area will be 24x26 and the garage will be 34x26 with the remainder being cold storage. I'd like to go with a 2/12 roof pitch on the addition to maintain some space above ceiling of the office and garage areas for storage and am struggling with how to do this. Here are my questions. Can I spray foam the underside of the roof instead of insulating the ceiling/attic area? Am I better off using a blown-in-blanket insulation? I'll probably need 14" i-joists for the roof if I go this route.

 

[u2slow]

I would figure out what sort of roofing material options 2/12 leaves you with. Low slope ***** - I discovered that with my car-port - and its not even insulated.

 

[golfnut]

Roof will be ribbed steel to match the existing roof. I've been thinking about it for a while now and have a plan formulated in my head. I'll meet with a builder after the first of the year and go from there.