Cardboard, hard Styrofoam board, hot glue, sharpie, paint, colored posters, sticks, clay, and household things.
Since they never sold a reasonable Cobra Headquarters playset, I decided to make my own playable Cobra HQ. It took me a good month and a half to create. It's definitely special, I made it my self. I also molded Cobra Commander's throne.
The Cobra Headquarters includes a laboratory, a prison, a meeting room, an intensive care unit, a control room, a bunk room, a weapon supply room, a vehicle garage, and finally Cobra Commander's chamber.