If you guys ever bother, if you check out my blog (down in the signature) and look up the old stuff, I tell how to construct basic hallways, corridors and well, rooms. It's all the same concept in the end. I buy the wood at Lowes. one of those big 8x4 pieces or whatever and have them cut it in half. It turns into a 2'x2' piece in the end. From there, I just plop in those wonderful metal L-brackets (w/ screws). Add foamboard of varying heights (dependent on what you need it for) and you're set. It's really that easy.
I don't remember how Luke does his but iirc, it's more complicated! Foamboard does warp so you just crack it on the side not visible and it should straighten out. Don't worry if it looks like utter crap. You can fotoshop out most of the inaccuracies. Seriously, you gotta figure the basic wall construction is easy and you can do tall, wide or big with them.
That ender to my War For Territory dio, that was a headache. I was using FULL pieces of foamboard (32"x24" or something) and bracing them on whatever I could so they wouldn't fall in. It was a 2-level set. It was an ambitious set but the final product wasn't so hot.
Just to note, I prefer to keep a very particular look to my dios. So therefore, for me to use plastic walls all of a sudden, it wouldn't mesh. And to a degree, the playmobil stuff doesn't always fit in. I build my own stuff; from steps to computer consoles. I HAVE gotten lazy w/ computer consoles and just go the Star Trek route where it's a screen on the wall and the people give it commands. lol.