Are you saying that the ceiling is in an 'unfinished state'? I mean, if the ceiling is in a finished state, what's having you want the ceiling insulated? Is it not insulated now? Is it insulated now but not adequately enough?
Understand that no matter what ends up happening on this particular job, the underpart of the roof (sheathing) should be vented. And to properly do this, you need soffit vents, soffit chutes, and a ridge vent. And to boot, if the insulation is too tight, air won't flow through the chutes and out the vent. Hence, you'll most likely end up w/moisture problems.