1. A roll of duct tape
2. A cardboard tube
3. Some sort of cardboard box
5. Compass (mathematical)
6. A rocket engine
7. Straw (optional)
Step 1: The Body
Step 2: Trim the ends off according to the length of your tube and how small you want the rocket to be.
Step 2: Adding the Fins
It's up to you to decide how you wish to orient your fins. I chose to use 2 sets of four. One large set in the back, and one smaller set in the front.
Step 1: Take your cardboard box and cut out a stencil for each size of fin. Make sure to mark these so that you don't accidentally end up using them.
Step 2: Cut out 4 of each size
Step 3: Cover the fins with duct tape. Fold the tape over the cardboard and trim off the excess.
Step 4: Attach the fins to the body. I recommend placing them about an inch from the bottom and/or top.
Step 3: The Nose Cone
Step 1: Create a double-backed sheet of duct tape that is about 3 strips in width and length (this means putting the two sticky sides together)
Step 2: Cut a circle out using a compass and scissors
Step 3: Cut the circle in half
Step 4: Curl the semi-circle up until the bottom of the cone is the same as the circumference of the top of your cardboard tube (until it fits snugly on the top)
Step 5: Attach with more tape.
Step 4: Launch Guide and Engine
Step 1: Cut about 2 inches off of your straw (or just roll one out of duct tape)
Step 2: Attach the straw between two of the lower fins.
This is used to guide the rocket off of the launch pad to help it fly with a straight trajectory.
Attaching the engine
For the size of rocket that I made, I used a B engine, and that worked quite well. It all depends on the size of your cardboard tube.
Take your engine and shove it inside your rocket. MAKE SURE IT FITS IN TIGHTLY. If it doesn't, roll some duct tape around it and make it fit.
I would suggest using Gorilla Glue to hold it in place.