this is a question for an engineer or architect. Yes, a roof can be built in the space available. But you've said nothing about the climate and snow/wind load so we can't design it for you.
btw, a gambrel roof [truss] may not be the correct solution -- such a roof fits into a semicircle, which would make it 12 feet high [plus thickness] at the top. Suggest you look into a flatter roof design with a hybrid truss or even [loading permitted] a flat roof [try a hip roof or low slope].
In any event, you likely need a building permit for this project and the permitting office will want plans, which their inspector will check for proper design [or proper calculations, or licensed engineer/architect endorsement].