Using a seam ripper, carefully remove the front pocket(s). The fabric will self heal - any tiny holes from the stitching will disappear with a washing or two.
Lay out the men's shirt with the shoulder seam slightly forward (as it would be if it were being worn). Place your pattern on top so that it is exactly centered over the buttons and is lower than the shoulder seams the amount that you will take up the shoulders (1 1/2" for my project).
Remove the sleeves from the remainder of the shirt. Lay them under the shirt so that they appear like this, making sure the shoulders of the shirt and sleeve are even. Using chalk or a fabric marker, trace along the line of the armhole and then parallel to the top of the sleeve. Then cut out the sleeve adding a 5/8" seam allowance to the armhole but not to the bottom of the sleeve. Use this sleeve as a pattern to cut out the other sleeve. If you are using a long-sleeved shirt, the process is the same, you'll just have to hem the bottom of the sleeve yourself.
Make the waist tie by cutting a strip of material 3 1/2" x 40". I didn't have one continuous strip that was 40", so I sewed two pieces together to create enough length. Fold the strip in half, lengthwise. Sew the long edge together to create a tube. Turn the tube right side out. Tuck in the ends and press. Stitch along one of the long sides of the tie and along each short end.