I am in the process of building a 30×40 workshop.  12′ walls.  2×6 construction on 24″ centers.  2nd story under the rafters….8×12 pitch roof using 2×10 lumber on 2′ centers.  Zone 4 in southern Illinois.  I will have two 9×8 insulated garage doors.  Concrete slab with radiant heating in the floor with 2″ foam under the slab.
I am looking for insulating advice for the rafters.  The 2nd floor will be, at least partially, an office with some sort of heating/cooling.  I expect the 2nd floor to be approx. 16′ wide x 40′ long.  will likely only cool half of that.  What would your advice be on how to insulate the walls and rafters?  the roof will be 5/8 plywood and then the “hidden fastener” metal roofing on top of that.  I do not like the “pole barn” exposed fastener look so I am going with the hidden fastener system and the installation guide shows it being placed on top plywood/OSB with a felt-type barrier in between.
I am not looking to cool the main floor as it will be a garage/workshop.  The radiant heating is mainly to keep my tools and the concrete from being cold in the winter…I will most likely keep it around 50 degrees in there.
Thoughts on closed-cell in the rafters vs having airflow and a vented ridge of some sort?  other recommendations?