need help building a skate/bike/scooter track

hey guys

we have a ton of families with little kids at our church (we are kinda sub par with only 3)
after church there is always a bunch of us hanging out, and all the kids have their bikes and scooters out, the teens are shooting hoops or playing basketball

this is all cool and what not, but the little kids always spill over into the parking lot and, really, it is just a matter of time before one of the little tikes runs out underneath a car

so, i came up with this plan...all we need to keep the kids out of the parking lot is putting in something they like better

so here are a few pic so you get the idea

(ok, pics wont load in the thread, they will be at the bottom)

the little square on the bottom right is where i want to put it...roughly 3700 square feet

the second pic is a place out in east lansing, that has EXACTLY what i want, but much larger
(that one even have a tunnel)

so...i need all your input
from what this might cost, what material to use, who to outsource it too, what to tell our insurance agent, everything

oh, and above all...designs
should i put in a cross over like a figure 8, or is that asking for trouble?