You can check out wikihow, they have plenty ideas for you to make sewing patterns from your original designs such as this site: http://www.wikihow.com/Make-Your-Own-Sewing-Patter...
Otherwise, taking a sewing class would be quite beneficial as you will be also learning the efficient and effective ways of making sewing patterns.
You could possibly be inspired to create more designs from the class that you attend to. Meanwhile, there's also opportunity for you to make friends with people who have similar interest as you.
People who attend classes are more willing to teach you about sewing a variety of patterns. Hope this helps!