I just finished building this particular launcher. I use this launcher with the paper rockets (guide here) and it works great. It's a little more advanced, and a little more expensive to build than the water rocket launcher (guide here).
Head to this page to get the instructions. You can also buy a kit directly from Maker Shed if you don't feel like getting the supplies yourself, but keep in mind, you will still need to build it. I was able to buy the materials at my local hardware store. Mine turned out to be a bit different than the instructions given to you at the link, but it works just the same.
Please remember to put duct tape around the air chamber. You never know if and when it will explode when under pressure.
