Airport Design

I am thinking about getting into modifing stock FSX airports or if that is not possible then designing new ones.
What program would I need to take a stock FSX airport that has no parking or limited parking and then add parking?
An expample is KRIV March JARB in Riverside, CA. The stock FSX airport has no parking so MyTraffic X will not park any aircraft there.
Rod
What program would I need to take a stock FSX airport that has no parking or limited parking and then add parking?
An expample is KRIV March JARB in Riverside, CA. The stock FSX airport has no parking so MyTraffic X will not park any aircraft there.
Rod