I would suggest Rigid Foam insulation. It is considered a superior insulator because it will not sag like batt insulation, and tends to leave fewer gaps, which reduces air leaks.
I like the idea of using metal for a ceiling but you will still need a vapour barrier since the metal will have joints (unless you are using one sheet that covers the whole ceiling ) I prefer 6 mil plastic instead of the paper since it is almost impossible to seal the paper edges and also the paper becomes brittle after a few years and easily cracks. I will be using a plastic vapour barrier and metal roof in my garage.
Edit: Sorry. Didn't realize this was such an old post.