As far as I'm concerned, most of the time, building a scenery has to be spent on the 3D Models (modeling and placing)
Modeling and texturing can be done by several persons at the same time but placing these models can't (not yet)
I'd say that 80 percent of the 3D Modeling is spent on painting the textures.
So if you really want to help, paint 512x512 BMP's for every building on the airport (No Photos and no Shadows please!!!)
The actual 3D Model is done pretty fast, there are a couple of free 3D programs like Blender and Wings 3D , but I'm using 3DStudio Max, which is quite cheap for noncommercial purposes. There are tons of tutorials for these programs on the Internet.
But painting the Textures would be really really a huge help!!
Provence 2.....all artwork