You are going to need:
-Old Mens (or womens) button down shirt
1.) First your going to take the shirt and cut off the sleeves from right below the armpit to about 2 inches from the top of the sleeve.
5.) Now that its the right size, time to cut the back like you want it. I kinda want mine to be subtle razor back.
6.) Now hem the collar and sleeves. I added a couple darts onto my collar.
7.) If you want to add more, you can add darts in the back. Just pinch and pin. Sew these with a 1/4in seam.