Yes it will be annoying, you need a Damp proof membrane which ill be a right mission! Drill holes in the roof for ventilation 😂😂😂

It can be done though but only if you use the cheap polystyrene insulation and cut it very tight fitting in between the roof rafters so you wouldnt need no glue to hold it up, then its easy enuff to put a full sheet of plastic covering it and then staple gun it too the wood rafters.. You would definatly need the correct tape also for the plastic and also cover each staple with that tape also so it wont ever let water vapour in behind it 😊