I would suggest you sew the 10inch squares together so you have 4 rows of 5 blocks in each row first. Then measure the length and width of that top. You will need to add 6 inches to the width and 6 inches to the length before you buy the backing and the batting Because it will need to be that big to quilt if you have someone longarm quilt it for you. I usually don't buy batting until the top is made and the backing is sewn together. Sometimes the longarm quilter will have batting she prefers to use on her machine. Of course any quilt shop employee can help you figure all this out if you are in a hurry to get everything bought while you have money to do it. Good luck.