Since I am a 1:600 collector I will say 1:600. But truthfully, 1:600 takes up the least space. I have a huge project going on in the basement for a 1:600 airport, but I own 150 aircraft. I have terminal space for 250 as of right now, but I am always changing my airport around every couple of weeks.
For runways I will be using roofing material, shingles etc. It is great for asphalt runways. My grandfather taught me that idea when he had a trainset and he used it for roads.
Buildings: As of right now I am using 2x4s, not decorated. My terminals are kind of like an Atlanta type terminal or new DTW terminal. In other words row terminals. Although for scale size I am using two "mile long" terminals of 2x4s.
I also have some round classic type terminals. The only thing round that I could find were used Remo drumheads from my drum set with clear tops. I guess it is a terminal with a skylight
When I get more time I am going to decorate the terminals to look real. I am going to paint windows on the 2x4s and do some architecture with thin plywood.
What a hobby store owner told me to use was plastic. Most hobby stores own plastic for custom made buildings for trainsets. It is thin and you can cut it with a knife. The hobbystore also sells tiny square tube shape plastic- think in other words a tiny square shaped straw, the size for drinkboxes but square. It is the ideal size for loading bridges for a 1:600 plane.
I haven't done anything with lighting yet.
Your best bet would be to talk to various hobby shop owners around your area. Most are willing to help, I would go to several stores just to get different oppinions and ideas.