Stupidly, I didn't realise that men's shirts have nowhere for your boobs to go. I thought to myself, "this'll be an easy refashion, just take it in a bit" *Insert deranged laugh here* I'm glad I had my trusty dressform to work with or this could have been a real nightmare. Next time it'll be much easier though, since I know what I'm doing. Sorry I forgot to do a proper tutorial, but this is how I did it.
I used nearly every scrap of fabric available for this top. I first removed the collar, cuffs and sleeves and had a good look. I raised the back, took in the sides, and added darts.
The bottom half of the sleeves became the Peter Pan collar. I used a template I drew specifically for this shirt. If you have a dressform, or a willing friend, cut the neckline as low as you want, then put the shirt on the form/friend, mark the centre of the back, and pin a piece of tracing paper around one half of the neck. Trace the edge of the neckline marking the centre front (or as far as you want the collar to go) and centre back. Remove the paper and draw the collar you want. For a Peter Pan collar, this will look like an upside-down comma (,) Cut it out and pin it to the shirt, checking it fits well and that the centre line is straight. Place the template with the centre line on the fold of your chosen fabric so when you open it out you have the full collar. When you cut, remember to add seam allowance. Cut 2 and add interfacing to one of them. Sew right sides together leaving a gap so you can turn it right side out. Snip all the curves, turn it the right side out, press and sew up the hole. Topstitch around the edge of the whole thing and pin it to your shirt. Hand sew with the most invisible stitches you can, and you're done :)
The cuffs became the scalloped placket (see the two little buttons at the bottom? They hide the old buttonholes :) To do this, I drew a template and made it in exactly the same way as the collar, minus the interfacing. I unpicked the buttonhole placket for the length of the scalloped piece and pinned the piece in place. It looked a bit boring, so I dug into my ribbon stash and found a piece of broderie Anglais edging to finish it off.
When I took in the sides I made the armholes smaller and reinserted the sleeves with a bit of puff. Finally, I moved the breast pocket to the hip. I kept the length as it was so it would be tunic-y and the pocket is so low you can tuck the shirt into jeans without seeing it.