This will show you how to choose materials and how to construct it.
Step 1: Body
There are many things that you can use for the body. I use PVC pipe but other options are: metal(light weight ones), cardboard, fiberglass, carbon fiber, and plastic. I use PVC pipping because it's easy to cut, fairly cheap, and easy to get. You will need one that is light weight and strong.
Step 2: Nozzle
When choosing a nozzle it can be hard. I use a wax/ and clay nozzle mix (I have an instructable on it) it works great for me and is very cheap and easy to make. Others choose to use metal, PVC, and clay. Using a metal nozzle is the best but I currently don't have the tools or budget to make one. With a lathe you can make or design one. The nozzle needs to be able to go to around 2,000F since Kno3 based propellants are around that. You can read more about nozzles and physics behind it on www.braeunig.us/space/sup1.htm or other rocketry websites and forums.
Step 3: Propellant
There are tons of ratio for kno3/sugar rockets but after 100+ test I still am finding new and betters ones. You can view my instructable about kno3/ sugar propellants for more information but this will give the basics.
A basic ratio is 65% kno3(potassium nitrate) to 35% sugar. Many additives can be added to reach and faster/slower burn rate and higher ISP. Additives such as sulfur, Fe0, and AL powder. I use sulfur in my fuel as it gives a bigger flame and faster burn rate( as my test show).
There are 3 mainly used was to prepare the fuel, dissolved and boiling, dry heat, dry press. I prefer dissolved and boiling because it works better but it takes much longer and if done wrong doesn't work as good. I would recommend dry heat for starters as it's easy and fast. My other instructable for propellants talks more about the methods of cooking it.
Step 4: Installing Nozzle,Casting, and Pre-launch
I install my nozzle by ramming clay and wax mid into the bottom. If you use a metal or PVC pipe you can also screw it on with threads or cement it on. I find my way effective and cheap. After installing your nozzle and making your propellant you need to cast it. If you choose to dry press it you need to ram it in the body or motor casing until it is solid and doesn't fall out. Casting it can be tricky as the fuel is hot (200F+) which will burn your fingers. I use a spoon to slowly add fuel into the top of my motor casing then carefully ram it to the bottom to get all the air bubbles out. If air bubbles/air gaps are there when launching it may cause it to explode. After you cast the fuel
Install it into your body and your almost done!
Step 5: Launch
When launching it find a flat area and either prop it up on a launch pad or set it on the ground. PLEASE LAUNCH SAFELY. Launch it not near buildings or other people. Also if it goes around the height of airplanes you need to contact local FAA as to when you can launch your rocket and not endanger planes.
Thank you for reading my instructable. If you record your rocket I would love to see it so just post a video in the comments.