The choice of a ventilation system will depend upon the size, shape and the material used in constructing the roof. Proper ventilation systems consist of vents and hoses in the roof such that there is balanced air flow under and over the roof. It is estimated that in a balanced air ventilation system for a roof, there is a requirement of one square foot of venting for every 250 to 300 cubic foot of air in the attic or the space immediately below the roof. This also translates to an appropriate number of vents within the roof. These vents range from static open units and turbine style ones to thermostatically operated and electronic ones. The choice depends upon how deep your pockets are and the size of the roof.