We have pretty much set our sights on the gambrel roof design with a pair of shed dormers (one at each side). I'm talking with concrete guys and truss mfgr's right now.
The gambrel is such a great design for many reasons, and since you have already built a similar structure, you know what to improve upon this time around. Plus, the most beautiful outbuildings in our region are old, gambrel roofed barns. I think it is a great choice for a secondary building (or in my case, the primary building

).