Replying to Possible Summer Setup Drop-in

So originally my friend and I were going to put in some turf on a slope which led into his backyard woods which we cleared out previously, but already roots and plants have grown back making it bumpy and kind of unusable. However, I would much rather make the slope at my place, and would be willing to as long as I don't need to build up an entire base for a drop-in. Here is the one place that could potentially bring enough speed for a good setup just by making a slope starting from either the top of the rock wall or the top of the wood shed. Just looking for feedback on whether or not you think it would be successful to put down plywood and turf to get enough speed for to slide up to a 20 foot rail. Hopefully the pictures below give an idea of the situation. Thanks!

[img]http://s31.postimg.org/abphmm76z/Photo_Jun_13_5_47_05_PM.jpg[img]

[img]http://s32.postimg.org/dsr36h4tx/Photo_Jun_13_5_47_28_PM.jpg[img]

[img]http://s32.postimg.org/mbjdd5lth/Photo_Jun_13_5_51_25_PM.jpg[img]

[img]http://s32.postimg.org/f9cpiukdx/Photo_Jun_13_5_52_00_PM.jpg[img]