since it is July it brings to mind the littke testing I did one year at county fair

about 2016 excebition hall got a new roof
and they removed all the insulation when they put the new roof on and they added none back when they put the new all steel roof on

144 degrees F when it was 88 outside

the very next building over had the rolled fiberglass in the house wrap type insulation under the tin
ceiling read 86 degrees with the IR thermomometer

the two buildings were 15 feet apart and it felt like you left an oven when you walked into the insulated building with big doors open at both ends from the uninsulated building , they tried adding 4 huge exhaust fans about 4 feet each they were basically just a waste of electric they only dropped it a few degrees.
had 3 big barn fans in the doors on the shade side moving cooler air in , still you cooked , it was radiating down from that 144 degree ceiling.

Do like wetdog said or save yourself a lot of trouble and put shingles on.Everybody wants metal roofs these days and I can tell you after fixing a lot of them I sure wouldn`t put one on any house or heated building now days.The screws back out from the metal expanding in about 10 years and then start to leak.Condonsation is a problem if not done right.If the screws are put in to tight the little ruber rings will be smashed and leak and the list goes on and on.

Stay away from synthetic roof paper in my option.
Ice and water is the only synthetic we ever used,,,,we covered the entire roof deck when installing tile on roofs in Alaska

A metal roof is only as good as the base material and flashing detail
the best underlay is torch or Peel and stick applied Modified, installed like it would be the primary roof
Standing seam roofing always applied directly to deck surface.

Ventilation at the fascia with insulation baffles and a ridge vent or eave vent ( not both)
Eave vents installed in conjunction with ridge venting will increase the possibility of mold to grow on the underside of the Plywood roof deck.