I make alot of T-shirt quilts and love when the pieces are NOT all the same size....it adds character to the quilt, in my opinion.
If you don't have a place to lay out all of the pieces.....get some graph paper! I cut out pieces to replicate the T-shirt squares (and/or rectangles). I keep it simple and use 1 square of the graph paper to equal one inch of the square.
Next, I arrange them on a full piece of graph paper, leaving some space between them, so they are attractive to me (like putting pieces of a puzzle together!).
Now count the squares between your pieces and they will tell you how much fabric you need to join the pieces together. (if you have 2 squares between the pieces you need to cut a strip that is 2 1/2 inches wide to get a 2 inch finished "sashing").
I hope this is not too confusing....if you have any questions please ask or PM me. Once you get started, you'll love it!!