Hi, Eric,
The buildings of the Playset are made of Foamcore, and the backdrop is made of Mounting Board. I created the decals using Photoshop and printed them onto A4 sticker paper.
I used a hot glue gun to "weld" the foamcore together. The 2 large sections of the backdrop have a hinge that is simply "invisible" sticky tape, and the hangar sections slot into place. The whole thing folds up and the buildings can all fit onto a small(ish) shelf.
If you want to have a go, I have posted instructions and my decal sheets here: http://www.flickr.com/photos/30029551@N06/collections/72157614158860278/
You can use just sections to build a smaller Diorama, or customise them to your own requirements.
The good thing about building stuff like this is that it doesn't take long to build. The whole thing must have taken me 2 days. (The decals too the most time, they took about 2 weeks to get right).