Most of the time I start with an idea and then go from there. Sometimes the idea comes from a picture of a finished quilt, a single block, or a pattern.
Honestly, I have never started with a pattern and finished the quilt using that pattern. Somewhere in the quilt pattern I decide I would rather do something else than what the directions say and off I go.
So...If you don't want to use a pattern, you don't have to, except if you are taking a class. They typically want everyone to do the same thing.
Classes are great. If you haven't taken a quilt class, you might like to think about trying one just to get into reading and using patterns.