Sorry, that slipped out. I have had chickens for four years now, they range freely all over the two-thirds of an acre comprising my property, and not a single chicken has ever gotten on top of my car. It's a Toyota RAV4. (No carport or garage here - I turned it into the coop.)
However, the "volunteer" peacock did perch on it one time (that I know).
They DO, however, try to get INTO it, and they often get into the contractor's van when he's here working on something.