I was also considering a different layout, with the runway. According to the fact that a 1:400 A380 (the largest model you can use) is 20 cm long, that the most important things in an airport are the spaces among parking stands and taxiway and among taxiway and runways, you could develop the layout in this way obtaining also a runway:
- 4 cm wide terminal building
- 4 cm for service road
- 20 cm of parking stands
- 26 cm of taxiway space (an A380 Is 20 cm wide so you have 3 cm tolerance in both sides)
- 8 cm grass
- 18 cm runway (about the runway there Is something to say. London LHR runway Is about 52 meters wide that in 1:400 are 13 cm. The other 7 cm are the space out of the runway).
With this layout you have space for parking stands, taxiway and runway.