I stared at the R.E.M. t-shirts and finally figured out where I wanted to start sewing the left half together. Sometimes this is the hardest part - to figure out where to start. For the right side I started with the black t-shirt in the lower right corner. I added the rust/orange shirt then the shirts to the left. I finished it off with the navy and gray shirts at the top.
For the left side I decided to start with the olive shirt with the orange star and the orange DNA looking shirt. I try not to have a seam that runs the full length or width of the piece. Obviously I will have one seam running the length, but it won't be a straight seam which will kind of disguise it.
I will continue to sew together shirts adding denim sashing where needed. I will also be roughly measuring as I go so the piece fits the size requirements. The last two years pieces could be 72" x 72" max. There was a piece last year that was much bigger than that so I guess there is some leeway, but I am not willing to take that chance and make my piece too big.