I’ve repurposed another shirt into an apron/smock (see the first one here), and whilst this one isn’t terribly different, I thought I’d give a brief rundown on how I did it.
You want a shirt that is a fair bit bigger than you, but not ginormous. This one is a man’s size medium. Look for one discarded by a family member, otherwise it’s a case of trawling the op shops. This one is quite a nice 100% cotton with interesting elements.
All the contrasting fabric was on the inside of the shirt , so I simply turned them over.
Cut off the collar, the sleeves and the yoke. You will be left with a body. This shirt had a strip of contrasting fabric down the centre back (sorry about the lack of ironing). I thought it would look strange down the front so I unpicked it and put it aside. 
The first thing you want to do is to sort out the yoke. I cut off the shaping, and took off the label. The yoke was much too wide for me, so I cut off one side and resewed the felled edge back on. This edge is where the sleeve had been flat felled to the body and it makes quite a nice finish when cut around.
The bottom of the yoke was flat felled to the shirt so I turn it upside down and this edge becomes the top edge.
You will need to now gather or pleat the shirt back onto the yoke. I sew right sides together and overlock, then topstitch. If you have a fun label, sew it back on to the outside. Not upside down like I did!
You can make the pocket out of anything, but my first one used the sleeve and cuff and I decided to do that again. The cuff was lined with plain black and the placket had a nice piece of contrasting stripe, so the sleeve was turned inside out. I cut down the sleeve seam and through the cuff so that it would all lay flat. I then laid the sleeve on what is now the front to get a nice shape at the bottom. Note that I took the photograph before I decided to turn the sleeve inside out.
Stitch the new pocket on, topstitching if you wish. Change out the buttons to make it all more interesting. Where I had cut through the cuff I turned in a seam allowance on one side, but on the other, which was joined to the sleeve seam already finished off with flat felling, I just zigzagged over the cut edge of the cuff.
I just noticed a massive thread attached to my leg! I considered cropping it out of the photo, but decided to keep it real!
To create the back I just crossed the two sides over until I was happy with the angles. I sewed round the top. I think I could have made the back a bit wider now that I look at the photos, but it feels fine. I struggled to get the back to sit flat for some reason, and even with a bit of help from Mark, I have a slightly distorted join. I decided to leave it.
The collar was also turned inside out and joined the front of the apron to the back, and that long strip which I took off the back was doubled over, zigzagged together and became my other shoulder strap. I zigzagged over some of the buttonholes with the red thread and basically fiddled around with finishing. When I went through my red button stash I found a large number of “buttons” that had circles punched through the middle. I found some red beads and sewed them into the middle of the circles anchoring them like buttons. I really like the effect.
Please note my little photo bomber. I think she thinks the camera remote is edible as she showed a great deal of interest in it.
This was a quick transformation, taking a couple of hours. It would be even quicker if I hadn’t done all the topstitching. It’s a really nice way to reuse old shirts that are too good for landfill, and I can attest to the fact that they really do protect clothing, and the enormous pockets are incredibly useful.