when GTI parked at angle, bad water leaks

i've got a 2002 GTI.

my driveway angles down at about 5% grade. if i'm parked in the driveway when it rains, the car (sunroof?) leaks - badly. i get a puddle of water on the floor on the driver's side even in a light rain.

no leaking at all when parked on level ground - no matter how hard it rains.

any ideas?

hmmm thats not cool, happened in my saab, but there were vents up by the wipers that led in towards the dash and drained into the car at an angle,
if i closed the vents and parked on a hill it wouldnt do it at all. Not sure if that helps at all but good luck