Mine go about their business in the rain, don't seem to mind it at all - stand in it, sit in it and roost outside in it (I live in the PNW and we get a lot of rain). It's the wind that mine seem to dislike and they'll go into the barn if the wind blows their feathers the wrong way
My Bourbon Reds love to roost high on top of the plastic canopy frame, where they're exposed to the elements and not in their cozy A-frame coop or in the fruit trees even. During the daytime I've seen them shelter a little bit to get out of the rain if it's coming down hard, but not at night when they roost. Many times I've found them sneezing with ice formed on their backs after a rain and a freeze. My fiance would try to wrangle them into the A-frame every night and also put up a big branch for them to roost in between the fruit trees, but they just prefer being together up at the highest point in the pen instead.