I did one that as large rectangles all the same size. Mostly from cut up fat quarters. I'd have to measure to get size. But it was mostly to practice on a new sitdown quilting machine. It's a fun quilt that I use a lot and is usually the one I take on airplane trips.
I think 10 inch squares could be great (also think of offseting them so you don't have to match seams)..... Then think about a fun quilting pattern to overlay them. And make sure you quilt close enough together.....