I fired up some doom level/texture
editing software and used photoshop to size, tile, and print off all the
textures I needed. This project needs like 10$ of ink btw. I cut them out
with scissors and/or an Xacto knife and a ruler. I glued them down to some
cardboard I got from an art store (ooh deluxe!) with a thin coating of
Elmer's crappy cow glue. Then I cut and trimmed the textured cardboard
walls in the same way.
Here's me cutting out and sticking the textures for the little platform where the Doom guy pics up the rocket pack. I used the file on my penknife to sand down the edges of each little wall to an angle so they would fit together better.
I used a glue gun to stick all the bits together. And I touched up the exposed white cracks with a pen. (That was a bad idea btw - a dark brown coloured pencil works a lot better).
I was sick of sanding edges down by hand, so I pulled out the dremel for all the other walls. I fit them together with the glue gun as usual. Yes that is a stolen cafeteria tray I am using.
My ghetto glue cooling method ;)