Insulating an open ceiling room

I have a small "studio" that has an open beam ceiling - there is no attic (or crawlspace) between the room and the roof. Since it has a small ridge beam (2x) there are rafter ties that run across the room, but otherwise, there is no framing structure at the roof.
I'd like to insulate this a bit and thought of putting insulation on the underside of the roof sheathing, perhaps R-11. I'm worried though that this will make the outside of the roof sheathing hotter, and thereby decrease the life of the roofing shingles. Is this something I should be worried about?
Also, when it comes time for new shingles, can I insulate the roof (exterior) and then put shingles on? If so, would this make it possible to add the insulation on the interior on the underside of the roof sheathing?
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