My original thoughts were to unpick the pants and use them as a pattern, but these are still more than wearable, so I decided to trace around them.
The first thing I did was to turn the pants inside out and to pop one leg into the other so that I could clearly see the outline of the back and front piece. I then pulled out the shape of the front and the back piece and used pins to secure it to the tracing paper and drew around the pieces. For the pockets I laid the paper over the pocket and felt the edge and drew around it. I did the same for the front placket.