How about adding some sheds or porches on the sides of the gambrel I think it really adds character. Here is a nice example.
Here are some links of old barns pretty interesting stuff.
http://www.picable.com/Nature/Landscapes/Round-Roof-Barn.225823http://www.thornhillauction.com/110306howell.htmhttp://www.yessy.com/EARTHSPASSION/BARNS.htmlI have a friend who built a totally full radius roof barn similar to this one which is arched but not a full radius. He is a framer by trade and used scrap 3/4 plywood off of jobs and made a template and cut radius sections from the ply wood and nailed and gluded them to create basically 2 x 6 round arched trusses.
http://www.preservationnation.org/resources/case-studies/awards/Bender_Farm.html