Sorry, but creating an airport with Afcad 221 is like creating it in the dark. IMO, best tool is by far AD
FX Airport Facilitator X of Flight1. It's a payware tool, but worse the price. It as interface with a WYSISWYG mode. That means, you see exactly where your runways, taxiways, parkings and so on are placed.
Have a look here: http://www.flight1.com/products.asp?product=afxv1
While creating an airport in the nowhere, you certainly have to flatten the area.
Bernard