Step 1: What you'll need
Step 2: Cutting the shirt
Draw a line straight across the top, just under the neck. Cut through both layers.
Cut about 1 1/2" off the bottom. Shirts can vary, so alter this to meet your needs. You'll be adding about 3" back on later.
Step 3: Cutting the second fabric
Cut two pieces, each 1/2" longer than your shirt is wide (for my shirt it was 18") and 3 1/2" wide.
Step 4: Making the braid straps
Braid together, keeping the wrong side turned in, if you have one. Pin the finishing end with a safety pin so it doesn't come unbraided.
Step 5: Armholes and neck
Turn the upper edge at the neck under 1 1/4", then turn the raw edge in 1/4". Stitch with a narrow zigzag to form a casing. Make sure to stitch all the way to the armhole instead of stopping at the edge of the casing inside.