Basic DC Circle Pattern - The double crochet hat pattern has been around for eons. It is also a standard mandala pattern as well. Once you hit the circumference in increases then just do rounds of dc in each stitch for a deep as you want the hat.
Magic circle Tutorial - this is exactly how I make mine. I've seen other tutorials where they start with 2 loops but I always just do the one. I also pull that first ch loop really tight. The only difference is that I do count that ch as my first ch, main