When we hand frame a cathedral ceiling we us 2x10s for rafters so there is plenty of room for insulation and air flow above. Lots of older houses have attic rooms with insulation stuffed up against the deck with poor results.
You could add to your rafters on the inside to give you air space. then you could use a vented drip edge and a ridge vent.
http://www.google.ca/search?q=vented+drip+edge&hl=en&prmd=imvns&tbm=isc h&tbo=u&source=univ&sa=X&ei=sEYRUNCJG6LtiwKU8oCADQ &sqi=2&ved=0CFcQsAQ&biw=1016&bih=523