There are a couple of threads in the costuming section on this topic already. Looks like the way to go right now is with the super deluxe rubies shirt, which isn't half bad. It has a few stinky details to it, but nothing you couldn't fix with a TINY bit of know how and a little time in the junkyard here.
If you're on a budget, even the cheapo rubies shirt isn't half bad, as they seem to have gotten the silk screen pattern down pretty well.
I think if you are going for a really accurate one, the trick is to buy an XXXXL rubies, and then modify it to fit you, and clean up the seams.
Good luck, and keep us posed on your progress.