Depends on how the attic and roof are ventilated. If you have a ridge vent, then the channel must be maintained between the eaves and the ridge. They make foam panels for that, then you can put insulation over it.
Tiling the ceiling is possible, but often not necessary. If you wish to do it, you need a vapor barrier behind the cbu. you don't want multiple ones, so you'd probably want to either use unfaced fiberglass, or faced that you slit to compromise it, then put plastic over it.