Building a MX Track - Little Help

I am sure there are million other forums, but I trust my WW'ers. I want to build an oval track with (4) burns and two table tops for my kids to learn how to ride a bigger track. I have no clue where to start, how to build up the burns or jumps for that matter. We are wanting to train them in the mechanics of hitting those things without a million other mx'ers around. We got the land, the dirt and a bob cat, just no clue where to start. We want to get them racing soon, but wanting to practice alot more before getting out there. I would love the input.