Here is how I did it:
1. I cut off the collar, the sleeves, and the waist band. I opened it up and matched the sides together. The arm holes became the inside of the legs. I then found that it was too skinny for my legs so I cut a couple inch wide piece and added it to the inside of the legs.
2. I used a pair of shorts to see how high up to sew between the legs. I snipped and sewed. I cut off the bottom even with how long the shorts were.
3. I cut the seam off of the waist band and measured around my waist. I pulled it tight so it will hold the pants up. I cut 3 skinny pieces from one of the sleeves and sewed them together so I had one long piece. I folded them in half lengthwise and zig zagged it to make the drawstring. I cut two holes in the middle of the waist band through one layer. I laced the drawstring through one hole and out the end and into the other end and out the other hole. I evened them out and sewed the back to create a circle with the seam facing in. I then sewed it onto the top of the pants.
4. I added an edge to the bottom and was comfy all day :)