I wouldn't cut the angle too sharp, you want as much space as possible where the rafter meets the wall for soffit ventilation..with a good 18" of overhand beyond wall, then add a fascia to help block the wind.
Yes, metal roofs can gather condensation, when the metal is cold and the air in the coop is warm and humid.
It would really help to see some pics of existing coop/run and sketches of how/where you propose to expand.