I cut the tee shirts at the shoulders and then down the side and cut out the sleeves. Then use a fusible interfacing bigger than the size block you want and iron it on the back side. Then and only then....cut the tee shirts in the size you want them. You can add sashing between the blocks or add some pieced blocks like flying geese to 4 patches, what ever you want. I make a tee shirt quilt for each grandchild when they graduate high school. They help pick the fabrics and colors and placement of the blocks. They really enjoy the whole process. It is something they will always have and something they helped design.