To calculate the elevation degree the rule is that the height increases with 10 meters over 100 meters with an elevation of 10%(5,71 degrees) but I think if we maintain a diameter of 100 meters with a 5 meter height than the elevation degree will be 11,51 degrees and that is 20% . A diameter of 150 meters and 5 meter height is 15% 8,51 degrees. That's 75 meter up and 75 meter down but to avoid any take-offs the upper(horizontal flat) part of the hill between up and down needs to be at least 50 meters.
Maybe you can try out in Sketch-up first a diameter of 100 meter and if that is too steep than you try a diameter of 150 meter with 5 meters height. Or you think 15% is also too steep?
