How chilly is chilly?
I would wait until the warmest part of the day and bring a warm basin of soapy water and another of plain clean warm water out to where you want to clean her. Also have one large and one small towel, an extension cord and a hair dryer. Soak the small towel in soapy water and start working on removing the mess. Once you get it all off, rinse the towel in the clean water then rinse her off. Then dry with your large towel. Hit her with the hair dryer to finish drying her and warming her up.
Then go get a hammer and fix your roosts so there is at least 18" between roosts if one will be higher than the others so the ones on top have less of a chance of dropping bombs on the ones on the lower roost.
This is one of the reasons I have all my roosts at the same height.
Good luck with the clean up and construction project!