Make sure that it is a heavy material so that it will lay properly. A US Army half shelter is perfect for this, as that is what Boba Fett wore in ROTJ.
I weathered it with cuts, sandpaper, fire and paint. I literally used a lighter to light the thing on fire and then put it out to have "blaster holes". I also used some brown, gray and black paint to mist the fabric and give it some dirt.
You can usually find a half shelter fairly easily at a surplus store. It is basically just a heavy green canvas. Another option it to go to home depot and buy a canvas drop clothe then dye it and weather it.....if you want a color other than green.