I know that not all of you will be able to go to a shop and buy a Pendulum due to different reasons, the main ones being:
-No shop near you sells them
-No money, as they can be quite expensive
-Are keeping your studies a secret
So all you need to make your own Pendulum is a ring (or key, pendant....) and some string (or a necklace chain or such). It is pretty straight forward really. You put the string or similar item in the loop of the ring or it's substitute. Then you must consecrate it then it is ready to be used! :)
When you first start using it you may want to use it inside a glass as this helps the energy moving it to be more densly packed so you get your answer faster. As when you make them yourself it takes time for them to adjust to your purpose for them. If the movements are tiny the first time you use it do not loose faith, this is common. It will just take a bit extra time to get going properly.
Also if you have a shaky hand this can cause problems with using it. Just try your hardest to keep it still and you'll find that it works.