I have a Dutch Colonial house with a third floor attic room that spans the entire length of the house. The previous owners finished half of it and did a very poor job. I am planning to gut and redo.

The issue is that they put paper-backed fiberglass insulation between the rafters with NO airflow or vents. I would like to redo the insulation with a vapor barrier and drywall interior. My question is, can I put a airflow between the insulation and roof plywood and vent it out the top with the type of roof vent the spans the length on the roof at its apex. And, can this be done with out ripping all the existing asphalt shingles?