A while back, I was considering constructing a roof top carrier for my Vibe. On paper, it had many of Frank's parameters;
"...try to find out just how small the vertical height could be while still being functional, and spread the width out to the drip rails (or door gaps) on each side,...the front would be the least influential of all the surfaces of the box...but have it extend the curve and slope of the windshield... Let the back of the box follow the template down to a point."
and it looked like this;
But then I woke up and built this: