a pile of snow that big takes about 2 minutes to push together - and you will be able to shape it better, that has too much kick/is too small
if you use that you have to break down the jump no matter what when you leave
it probably will push out easily when you hit it
in this fucked up world of litigation we live in today if you were in a public park and someone else's kid hits the jump and gets hurt, you could be held liable as the owner and dude who brought the jump to the park - just a thought.
Depends on how much snow there is. If there is a few inches bring the ramp, a few feet bring a shovel.
I used to ride on a skate ramp similar to that one on a hill with just enough snow to cover the ground, it was fun times.