Its almost impossible to program hills - the hill I use has 3 different variations, one of which I've seen people almost pass out after 3 sprints up. Not the "man, I'm out of breath" but the "cannot walk due to legs shaking and body shutting down" kind of pass-out. 20 yards to the left, 10-12 hills is pretty doable for someone who is reasonable shape.
However, this is what you can do: base it all on the number of sprints/runs up the hill: have a light day, medium day and a heavy day. Increase these every 3 weeks or so. At some point, you have to stop increasing so also set a limit.
Light day - 8
Medium day - 10
Heavy day - 15
This is just an idea.