metal roof replacement ventilation

I have to replace an existing metal roof which was put on with no ventilation. The room below was insulated with spray foam onto the plywwod and rafters with no ventilation and can not be replaced without removing the existing drywall cieling. With no ventilation, the existing metal roof rusted away from the underside and must be replaced. I understand that I must have ventillation for the replacement metal roof but can not find any type of breathable membrane to allow the new roof to breath. What material can I use?