Ok, so this was freehanded and I had no pattern. I cut it apart, sewed some things together tried it on, sewed some more, tried it on again, sewed some more until I was done.
I tried to outline a little of what I did but even after I drew it up I kept remembering little things I did like ties on the shoulder straps because they were a bit wide. Also note that for the front top I did a lettuce stitch and then use some thin elastic to make it gather and fit better.
A few posts back I linked to some resources for sewing and DIY fashion. There are a lot of tips and tricks that may help you refashion an old or large t-shirt. 🙂