Poleshed making into shop need truss help
IMO: Definitely a problem. This building was built to hold up the current roofing material, which you didn't state what that is. Having trusses eight foot (8') on centers sounds as if it currently has a metal roof laid on stringers. Having 2x6 rafters with 2x4 joists sounds as if these are manufactured trusses also. If you are a competent DIY carpenter, you could build new, additional trusses "in place" so they are on twenty-four inch (24") centers, and use 2x6 joists. Or, you could tear off the existing roof and start over. I'd build the new trusses in place, myself.