Decide what slope you want away from your build in all directions.  I would recommend you go and look at other buildings or situations.  If you have a transect, take it and shoot it.  You want the water to drain in all directions.  You can never raise the building, practically speaking.   You could always bring in fill around a building if you got it to high. 

Personally, for that size of a building, and I was starting with a flat piece of ground I would build up the building sight with a min. of 2 ft if fill dirt and then slope away from that 2 ft of fill to gain your desired slope. 

Yes, take the stumps out.