I really tried to get a tutorial ready with photos and everything, but it's just not happening. So I'll give you a very brief tutorial. Finished size is 63 x 87 - a perfect twin size.
What you'll need to cut:
70 shirting blocks - 9.5 x 3.5" (9 x 3" finished)
63 white blocks - 9.5 x 3.5" (9 x 3" finished)
6 sashing strips - 3.5 x 57.5" (3 x 57" finished)
2 borders for top and bottom - 4.5 x 57.5"
2 side borders - 4.5 x 89.5
I used 10 or 11 XL shirts (not including the white ones), but didn't use up all the fabric in them. You'll want to check the shirt for holes, worn spots (elbows), and stains.
I used the shirt front without a pocket, the sleeves, and the back. The back has the most fabric, so if you don't want to mess with smaller sections - just start with that.
I also strip pieced. So instead of cutting a block 9.5 x 3.5" I cut a 20 x 3.5" long strip. I sewed 6 of them together (shirt, white, shirt, white, shirt, white), pressed the seams, then squared and cut them into 2 sections 9.5" wide.
If you were going to use non shirting fabrics you'd need:
3 1/2 yards sashing and borders
2 yards total of 8-10 different fabrics
or 8 1/4 yard cuts
or 10 fat quarters