A couple things to bear in mind:

1) The Great Wall wasn't built all at once; it actually consists on many different walls, built by different Emperors (and I think even two different dynasties, but I can't remember for sure.) Your wall probably wasn't built and conceived as a complete system, either, so feel free to make layers of walls to represent the changes that took place as the wall was constructed.

2) Ascension has some good points about the targets. Walls designed to stop armies are different from walls designed to stop people. If you're trying to stop armies (or horse-borne nomads) then large stretches of gateless, unfortified walls might work well. If you're trying to stop people, then you'll need garrisons, which will need supplies (probably near roads or rivers where food and other supplies could be more easily transported.)