Not a lawyer but have spent quite a bit of time trying to understand copyrights (especially since I worked in the creative department of an Advertising Agency early in my career. Some people might disagree, but the primary issue is not "personal use" but whether you are commercially using (including teaching) copies.
I think the purely legal is that if you can draw it, you can make it for personal use. Just like you can buy a book about settings and use those ideas however you want. Or, "public domain" designs like (traditional) log cabins or 9-patches. You can copyright the directions but not the block itself.
I can draft up any design, but if I'm outright copying someone's work, I go ahead and buy the pattern. I use the Hazel Hedgehog pattern of an example where I've both drawn it out myself and bought the pattern. There is nothing new original in my abilities to draft patterns. There is a lot original in Elizabeth Hartman's design.
When I show quilts, I do list an "inspired by" if I was indeed inspired by someone else's work. Just like I would list a pattern (or kit).