I made one with just cutting out squares, laying them out, laying the white stipes on top of them, and then trimming the big squares. It was easier than when I tried to do the individual triangles around the stripes. I laid an actual flag on the table to use as a template to match the angles of the stripes and placement of the squares so that the proportions would be correct.
Good luck. This was my first quilt and was a lot of fun.
Photo attached.