I build a LOT of paper rockets. I like to use them in competition because they are cheap, light and if I don't get the return, I'm not really out much except a couple sheets of cardstock and the time involved in building it. Plus, since you print your graphics/paint scheme right on the cardstock, you can pretty up what would otherwise be an unpainted rocket, not to mention making it easy to add my NAR number or name to the rocket.
The first two photos are some of the paper rockets I've designed, built and flown successfully. The last is Fliskits' Midnight Express, which I "repainted" (on the computer of course) to use the Estes Goblin's paint scheme.