It’s a bit of a worry that your roofer hasn’t specified exactly what he needs you to get for the job.

However, a breathable membrane won’t work as a vapour control layer as this needs to be completely impervious to moisture. It is possible to use foil faced insulation as the VCL but this would involve careful sealing of the joints. The easiest, and most foolproof method, is to use a thin plastic membrane. You can get this from a builders merchant, just ask for vapour control barrier.