I would first determine what size you want the quilt to be. then divide the width to come up with the size and number of blocks you would need. then depending on the size of the block you need, figure out what size logs and center you will need to create that block. On the length you could make as many blocks as you need. Don't forget to figure in borders if you are going to use them. Log Cabins are one of my favorite patterns. Have fun! Lucky MIL!