I use two metal rulers, one 12 inch and one 36 inch. You will want the 12in one now and the longer one when you are cutting the covering. Get the metal ones, you can use them to guide an X-axcto blade.

As far as building surfaces, I also use the Hollow core door and the 1/2inch drywall. It is a little harder to puch pins into the D/W than a ceiling tile, but they stay where you put them. The door is even cheaper if you snatch it from the neighbor's trash,(I still haven't figured out why they threw it out). I also have several pieces of aluminum angle (about 1 in long) that I use to hold pieces upright.