I think I'll be covering the panels fairly clumsy.Hoover the roof first, or give it a good going over with a hand brush. I then wash my roof a couple of times rinsing thoroughly each time and then make sure it's dry before applying the proofer. Try not to overspray the proofer on to the windows and body panels, if you are clumsy you may want to cover the bits of your car closest to the hood!
Worked OK for me the last 5 or so years.