An air space directly below the metal sheets with a vapor barrier, and that air space open to the outside at the eaves, will solve the condensation issue as well as afford some insulating value - how much r-value depends on what you build the barrier with.
In my example I applied Reflectix (brand) insulating wrap to the rafters, taped all seams, then came the 1x4 roof strap perlins then metal roof sheets. Exterior air can circulate through the gable edges between the metal roof and insulation, clearing any moisture that may leak into the 3/4" space from the coop below.
Reflectix, if you're unfamiliar, is like 1/4" thick smooth bubble-pack with each side coated with aluminum foil. It's R-value is best with an air space between it and any sheathing.
I also covered the inside of my coop rafters with chicken fencing too, to keep the birds from pecking apart the shiny aluminum foil from the inside.
In your case, taping Reflectix strips between each rafter on the inside against the 2x4 straps (leaves 1 1/2" air space) making sure to tape seal the edges well (tuck tape?) to the rafters, would give you R-value and vapor barrier. Then the trick will be to drill a few vent holes, at both the exterior "gable" walls between the roofing perlin 2x4s, through to exterior air, and cover with a bit of bug screen to keep them from plugging up the vent space. A 3/4" spade bit, with 3-4 holes per space, would work.
See photo, how I built my a-frame coop. The reflectix also helps in summer, keeping the heat down a bit inside.
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