Well, you should definately make it on a filled island or peninsula, like Chek Lap Kok or Kansai. The terminal should be in the center, with two pairs of runways on either side (lets say those runways are going north-souh) and a pair of runways (east-west) running lateral to them. The terminal's design should be something essentially like the one at CLK: All the piers (if there are any) should run into a main one that goes straight to the Pickup/Dropoff area for cars. The piers should preferably run at a diagonal angle to the main one to maximise passenger-flow efficiency. The Pickup/dropoff road should run laterally to the main pier, with the dropoff area on top and the pickup area on the bottom. This is to prevent any passengers from getting soaked in case they have to wait for a ride from the airport. Most airports already do this, though. Cargo, Maintenance, and Long-term remote parking facilities should be parallel to the north-south runways. Rental car facilities should be in back of the main pickup/dropoff road and hotel facilities in front of that. A shuttle tram should run from the hotel facilities to the main terminal, stopping at the car-rental facilities. A light-rail station to the city should be at the beggining of the tram line.
As far as the design of the terminal goes, It is up to you. I recommend something unique, but functional (duh). Today's architectual designs seem to dictate that one cannot go wrong with steel and glass, so I think it should be made of that. Light should be able to flow in from all sides and maybe even the top. The buildings should be irregular, in which i mean dont just have it be a box, however ornately detailed. the gates should have dual arrival/departure levels, and if you want to go crazy, make some gates that you think could accomodate both levels of the A3XX at the same time. Thats pretty much all i have to say. Damn, i wish i could do this kind of project for my high school! Id probably design a new San Diego International Airport. It's so crappy here right now.