Your roof insulation and ventilation are items that get a lot of discussion but are not typically going to have an effect on any real type of savings.
Roof insulation and attic insulation are two different things entirely. Roof insulations consist of foam boards that get placed on top of your roof deck and then the roof is applied over it. It is typically used for flat roofs in commercial type roofing because it is not a surface that other types of roofing can be applied to. If your roof is not a low slope or flat roof and you have attic space between the insulation on top of your ceilings and the backside of your roof plywood decking, this roof insulation would be of no benefit to you.
Roof ventilation is meant to vent the area between the roof surface and the ceiling insulation you have in your home i.e. your attic. You can always add more ventilation to your attic but as a measure to save big on energy costs, it will not prove itself out. The better way to consider additional roof ventilation is to weigh the impact of maintenance and damage during storms with how you choose to think about it. If you want it, then get it for no other
reason than that.
The idea of saving on energy costs begin with additional ceiling insulation being blown in by a licensed insulation contractor and attention paid to your windows and door openings. Be careful about cluttering the outward appearance of your home with materials and products that satisfy concepts but do not guaranty worthwhile results. It is our opinion that your roof should look how you want it to. It is an accent to the structure and it is what tops-off the exterior of your home.