Firstly I cut the shirt in under the armpits and shaped it slightly with two darts at the back and four at the front (two small darts either side of the pockets that I wanted to keep). I also unpicked the pocket flaps.It ended up looking like this....
I then cut a waistband and waist ties from one of the sleeves. My waistband was 8cm wide. I sewed the waistband on like I would bias binding, inserting the ties...
And the result!


