Anytime you have a higher elevation adjacent to a structure you will have to accommodate not only the direct flow of rainwater, but also the slow seepage that will find its way to lower ground.
Even a gradual slope will mean a lot of surface area/runoff.

I would suggest that you install some type of drainage system to draw that water away from your building [img]/forums/images/icons/smile.gif[/img] A gravel filled french drain sloped to either end is easy enough to do now while you have good access.