Decks, Patios, Porches and Docks - Ramp to Storage Shed

I know this is the deck forum,but I didn't know where else to ask this question. I had a new storage shed (20x12) delivered and there is about a 3 foot drop from floor of shed to ground level. I would like to buid a ramp so I can get equipment (tractor, snow blower etc) in and out without having to lift them in. What is the best way to do this? What are the best materials to use (treaded, exterior plywood etc.) Thanks.

If you want it to last, use pressure-treated wood imprinted with the American Wood Preservers Bureau (AWBP) stamp by a name-brand manufacturer like Weyerhaeuser, Georgia-Pacific, etc. for top-of-the-line quality control and 50-year limited p-t wood product warranties.
You can use three sloped 2X8" runners attached below the shed door(s)and nail 4' 2X6" boards across them for traction (16pd nail gap between them), or use 3/4" p-t plywood and screw two wheel rows of strips on it about 6-8" apart for traction when wet.
You can figure out the length that you need for the runners by pulling a string or tape out to look at the angle that you want from the shed floor level to the ground.
Leave the thickness of the decking above the runners at the top so that it comes out level with your shed floor.
For general illustrated how-to info go to http://www.bhglive.com/homeimp/ and click on "Decks".
Good Luck!
Mike