No insulation or barrier

I'm installing galvanized b deck on metal beams spaced 5 feet apart over my garage which is attached to the house. It will be a straight shed with no hip. The bottom and top of the shedded roof will be screen,not sealed to the outside weather with the feel of a covered screened in porch.. the garage has a cement floor there is a washer and dryer in the garage,vented. How much dripping should I expect'? I expect foggy days to be my problem, no snow here..