Building a log cabin. Have installed a steel roof on 1x4 stapping which is on top of the 2x10 rafters.

How would one finish the under side - insulation etc. The ceiling will be 1x6 T&G pine directly on the underside of the rafters.

Should I spray foam directly to the roofing- what thickness?

Or should I create a channel from eave to ridge for ventilation and then install fiberglas insulation?

Where should a vapour barrier be installed?

This cabin will be mainly used in summer and fall with a few winter weekends.

Any help would be appreciated.

Thanks Jerry