Jim,
Too many unstated items in your brief description. What kind of roofing material are you going to use ? Would recommend a standing seam metal lookalike (strips are 36" wide, not 12" eventhough they look like 12"). Lightest, cheapest and from the right manufacturer has 100 yr warranty on the metal, 20 yrs on the electrostatic paint (many colors available). More detail if you want.
Now the walls. How are they presently insulated ?
Have you installed air stops around the windows and doors ? Where is the existing moisture barrier ? With this info in hand you may be able to make a wiser choice on how to improve the wall R factor.

Deralte (aka Emmett)