For a one time piece of fabric you can buy your fabric such as muslin or a light colored solid, then sketch out your motif. In your case, your son's school logo. Color the logo in with the fabric coloring paint or pen of your choice - there are many excellent ones out there and several threads about them. Repeat the logo until you have your fabric covered. When you are making your own you can make that logo as large as you want and the spacing between as large as you want. You can have one only on the back of the quilt, or you can have one that is 20"x20" with 2" spacing for the length of the fabric.Whatever you design. Only you know what you want the finished fabric to look like. The sample logo is the hardest. After that all the others are simply repeating what you have already done before, exactly like making blocks for the quilt top.