Have you seen the "Too Cool T-Shirts" site? (for some reason whenever I copy/paste the web address in here the link doesn't work, but it's www.toocooltshirtquilts.com.
Their blocks are not the same size, nor is there any sashing. They have a book, but if you don't want to buy it, perhaps you can use the pictures for an idea of how to fit your tee shirt blocks together. Check out "The Process" (button on the left). Pretty neat.
My kids say they don't want a quilt made of their old tee shirts, but I've been saving the shirts in case they change their minds :).