Replying to Build a Step Up

any tips? by where i live there is mailboxes covered by an open building. its maybe 10 feet high. there is a snow pile from the plow that is about 6 feet, but there is a good 5 foot or so gap between the building and the snow pile. i was thinking about gettin a car tow down the street, and make the snow pile into a ramp. i dont know how much speed i need, or the how big the gap should be. i can post some pics later. any tips would help.