Here is my first go at this. I wasn't completey sure about the shape of the land, so I just did this... Also, will the car park be dirt? and do you want a Pit Lane type thing? The Red indicates the pit area, where the cars would be kept, that orange indicates the barriers or net fencing, not sure if you will use barriers. Anyway here is the design, I tried to make the Hairpins wider for more overtaking opertunites and extra racing lines, hope you like it