I normally use a pattern except when I have a panel or am doing a memory quilt. Then I just cut the panel up lay it out and put all kind of blocks and borders to fill in. If my blocks don't fill in completely then I just put some filler - could be a piece of fabric, checkerboard pieced, etc. Math is not my strong suit so when I do that it is usually by the seat of my pants but has always worked out. Since I don't really enjoy setting down, graphing & mathing I am more than happy to pay for a pattern. I figure it is money well spent.
BTW Kpross - yours is great!