Hi, I have made lots of t-shirt quilts and I always tried to make them the same size. Then I realized why limit ourselves. The width of the blocks need to be the same size but the lengths don't . I usually measure and find the biggest design and make my plans from there. Say the biggest block is 18 by 18. Then you make a row with all the blocks 18 by 18 or how many rows you want that size. You can have the other rows 18 by 10 or 12. Just make a whole row the same size. You could make them all different sizes and make borders for each block to make them all the same size. That would be more work but will turn out nice too. I sometimes applique some of the little tiny logos here and there on the borders or on the plainer blocks. Be sure to use iron on stabilizer on the shirts before cutting them out. It will give you more accurate sizes and stop the quilt from stretching later.