When I do follow a pattern, I rarely follow it to the letter, and this would be partly because I think I know an easier way to do it ('think' being the operative word here, doesn't always turn out to be true), or because I've made a mistake and have to undertake some creative bodging to get to the end result.
But having to make up a design entirely from scratch is still majorily out of my comfort zone and I don't feel these quilts are generally very successful. I ran a mystery medallion quilt project with my group last year, we started with a centre block and then I set rules as to the dimensions and theme of each border, but people could use their own fabrics and do whatever they wanted. Of course, this meant that I also had to make a medallion quilt, and apart from deciding to use my blue & white fabric collection, I felt very much at a loss particularly as the quilt grew and grew. I'm still not very happy with the result, which has a 'Blue & White China' theme, and it isn't quilted yet.