ᐅ Breathable vapor retarder or polyethylene (PE) sheet with ventilation gap

Hello everyone,

We are now working on the roof insulation and have planned the following build-up from the outside:

On the sloped ceilings:
Tiles
Breathable underlay membrane (vapor permeable)
20 cm (8 inches) glass wool insulation (directly against the underlay membrane on the slope without ventilation)
Breathable vapor retarder
Counter battens
Drywall ceiling

In the attic:
Tiles
Breathable underlay membrane (vapor permeable)
Unheated attic space
Tongue-and-groove boards
20 cm (8 inches) glass wool insulation (directly against the boards without ventilation)
Breathable vapor retarder
Counter battens
Drywall ceiling

First question:
If the breathable vapor retarder releases moisture back into the interior during the summer, wouldn’t the moisture accumulate in the drywall ceiling?
Should the drywall ceiling be ventilated in any way, especially in the bathroom?

Second question:
My roofer recommends a different setup. Instead of the breathable vapor retarder, use a normal PE foil and provide ventilation everywhere with a 4 cm (1.5 inches) air space. This means enlarging the rafters (currently 20 cm).
Which solution do you consider better?

Best regards and many thanks for your answers