Instructables
My wife says I always "ramp it up" with our boys.  Well this time she's right.  I built a sledding ramp with starting platform for our backyard.  I used 10'x 2" PVC for the ramp with 2x4 every 16 inches.  4x4's cut on an angle are used for supports.  The second picture shows a step up for the little guys and plastic cardboard all the way down the ramp so that other sleds can use it.  The handles are from Lowes and help give you a nice start.  The kids love it and it gives them enough speed to really enjoy sledding.  

 

haha...awesome