Have you verified whether you need additional attic ventilation or not? A good way to tell is to stand beneath your attic access door on a hot summer day. Open the door and if you feel a rush of air swirl around you and race into the attic, it is a good bet that you need additional ventilation.
Florida building codes require some attic ventilation unless you utilize a spray foam system that seals your attic from outside air completely making it part of your air conditioned barrier. For most of us, we have soffit ventilation around the eaves of our homes.
By and large the soffit ventilation serves as ample venting but does not move much air continually. You can use power attic ventilators to generate additional air flow but it requires electricity to power them. The other ventilation systems are called passive vents. As the hot air rises, it escapes out through these vents as it is replaced by the air entering through your soffits. These vents are called ridge vents, off-ridge vents and dead air vents or passive vents.
Any roofer will be glad to sell you a ventilation system because they are money makers for the roofers, but you should realize that what you are agreeing to is putting holes in your roof. You are breaking your roof system and relying on the sealants and flashing details the roofer has to use. Metal vents rust out and are prone to damage from wind born objects in storms. Wind driven rain can be forced inside creating leaks and they all require some substantial maintenance at or about the half-life time frame of your roof.
your old roof utilized them, then feel free to replace them with like vents or change the vent system altogether when you replace your roof but do not expect additional venting to change the temperatures of your attic dramatically. This will not happen. Your attic is going to be hot in the summer and cool in the winter. Big roomy attics feel a little cooler in the summers than do the smaller attic spaces. This is only due to a larger air space and the ease of your movement in it. Your insulation is on top of your ceilings to prevent the attic temperatures from impacting your home. The greatest impact on the temperatures inside your home comes from your doors and windows. Add ventilation because you just simply want to and not because you expect a greater difference in the conditions you