I have been making these bags, a little obsessively.
1. Begin by choosing two shirts that complement each other. (For me, incapable as I am of committing to any decision, this is the hardest part.)

2. Iron them!

3. Using a buttonhole as the center, cut a rectangle about 18 inches wide and deep enough to include the pocket of the shirt. The exact dimensions of this piece can be altered - as long as the other pieces match. (click image for helpful notes!)

4. Lay the cut piece on the other side of the shirt front, lining up the buttons with the button holes, then cut around, so they are the same size. Let's call these piece A (with button holes) and piece B (with buttons). Eventually, they will form the top of the bag.



5. From the back of the
second shirt, cut a rectangle (piece C) the same width as piece A and piece B (18 inches, or as wide as you made them) and long enough that piece A + piece C + piece B = approximately 32 inches. For instance, if your piece A and piece B are 18 by 8 inches, your piece C should 18 by 16
(8 + 16 + 8 = 32)

7. Repeat steps 3 through 5, beginning with the second shirt.
7a. Optional pocket - to convert the existing pocket, sew along the open edge, reverse-stitching 1/2 inch at each end. Use a seam ripper to open the upper seam.

8. With right sides facing, sew the long edge of piece A to the corresponding edge of piece C, then the long edge of piece B to the opposite edge of piece C. Sew up the edges. Do the same with D, E, and F.

You now have two pouches of the same size - about 17 by 16 inches. Lay them side by side, inside out.
9. To form a flat bottom, flatten the corners and sew across the corner of both bags, as in the picture. Snip off the corners.

10. To make the strap, cut a strip about seven inches wide and about 40 inches long. Shorter, obviously, if you want a shorter strap. This 7 x 40 rectangle can be hobbled together from odd pieces, and you can sew it however you want - odd angles and varied fabrics are good. Fold edges to center then fold in half, pressing and pinning to set the shape. Sew the length of the strap, near the edge, then back about a quarter inch further in.

Insert an end of the strap between the inner and outer pouch, at the seam, and pin in place. Do the same with the other end of the strap - from experience, I say,
make sure it's not twisted.
11. Sew the pouches together just below the buttons, turning and sewing up to the edge, then reverse stitching back every few inches, being careful to choose places between the buttons/button holes on both sides of the work. (Click the picture to see possibly helpful notes.)


Reinforce the straps by sewing twice around a box where the strap is attached.

Finished!
