It sounds like a great idea. I would do step one with the fabrics, laying out the big panel and the surrounding panels, leaving space in between for the window sashes. Try it both with all panels of one size together, and with the sizes mixed. When you like how it looks, move to your graph paper.
There are lots of panel quilts patterns and T shirt quilts on the web you can look at for help. And post a pic when you are done!