I have never bought and followed a pattern. I have used a pattern for a block to make my quilts...so it's not like I'm completely designing all of my quilts or anything. I "tweak" an existing block pattern to suit me... I have also looked at a quilt I like and figured it out on my own, to suit my needs.
The only pattern I sometimes follow, is the one I draw on my graph paper before I start a quilt. LOL I actually spent the afternoon working on my plan for my next quilt. I pulled fabric from my stash, measured and started calculating and measuring, drawing and colouring. lol