These instruction assume an intermediate to advanced upcycling experience.
1) Measure your chest circumference under arms. This will be the measurement you will use for the top of your tunic. The under collar and collar of the dress shirt is your bodice, and must extend a bit under your arms so that the flaps of the collar can fold down to the right and left of you straps, but are not lost under your arms.
2) Cut off the sleeves for pockets* in #4, or set aside for straps.
3) Cut the top of the shirt using your chest measurement + seam allowance. Add two front darts and two back darts to achieve best fit.
4) The side seam of your tunic and pockets will need to line up, so start by cutting 4 pocket pieces from the tops of both sleeves. Use your hand to determine shape, with thumb positioned at the top of the pocket with side seam at your wrist. See illustration. My illustration should have shown a deeper pocket, so make as big and deep a pocket as the sleeve allows. You can reduce if necessary later.
5) Try on top to pin sides and adjust darts. Give enough room at the hips for pockets. Once you have the right fit across the chest, baste sides graduating from the waist out to the hem of the shirt, creating as much as an A-line as possible to accomodate pockets. Try on again to adjust fit and find your pocket placement. Pin where you want the opening of your pockets to be.
6) Open garment inside out and place pockets on marked side seam, with pockets pointing inside of garment, and trim pocket and side seams to match. Rip out basting stitch and place pockets inside body of garment right sides together, pin pockets to side seams, and stitch, both sides of pockets to both sides of side seam. Open pockets out, right sides together, and stitch final seam down side seams and around pockets to hemline. If this is confusing, it is. You might want to google a 'how to' You Tube before attempting.
7) Lastly, roll hem the top of your tunic all the way around. Open the bottom seam of the collar and under collar piece, and tuck the front of the tunic into this 'bodice', matching center seams, etc. Stitch closed. Make straps with leftover side seams (or if you did not make pockets, use the sleeves), and pin to fit, then sew.
Good Luck! *Alternatively, you can add outside pockets as i did on the Blog Post picture.