Why not get a cat to sit on the roof and wait on Rodney Rodent to come out? If there's no food or water in there he won't stay there long.

I have the same problem with my old Ford. It rarely gets driven and every fall the field mice look for winter quarters. I turned on the heater the other day and seat stuffing flew everywhere!! Unfortunately our resident feline is too refined to catch mice, so my stategy is to place traps around the garage and recycle them to the food chain. Check traps often, a decomposing mouse is sickening to deal with!!