HeathRI do some dirt work design for parks so I spend a lot of time measuring slope angles. The best terrain for park building is surprisingly flat. A lot of parks are not built on an ideal pitch. This is usually overcome by changing the design of the features. If you had the luxury of choosing the pitch, 12 degrees or even less is pretty ideal for a flowy rail section. For jumps 15-20 degrees makes it easy to build a nice hybrid style jump line.
Damn that sounds like a sick job. Who do you work for?