Not everyone has the skill or ability to build things from scratch. Fortunately there are science kits available to help out! I posted this a few weeks ago after seeing it in the store. Water bottle rockets are relatively easy to make, but sometimes a kit is easier and simpler, especially if you are giving a gift to someone. Here's the one we found, but I'm guessing there are several others if you do a simple web search.
Water Bottle Rocket Kit