I use excel to design my quilts. At least the ones that have only squares to them. It's easier to use it than it is to do them by hand on graph paper as far as changing the colors. I can't afford any other program yet, so use what I can.
I also figure out how much fabric I will need of each color (Another con on excel is it's all in solid colors) as I have a chart I also use that tells me how many particular size squares I can get in a yard of fabric.
If you have questions PM me and I'll help you out.