Once again, I use black out cloth, available at most fabric stores. It would take a little sewing to get to your dimensions, but I RARLEY notice the seams. It doesn't take anything special to sew it excpet enough room to feed all that cloth through, so the dinning room table came in real handy! An alternative to cut down on the sewing is use velcro for attaching to the frame, but you would still want to sew the strips together.
The picture is GREAT for outdoor use and stores nicely. When I unfold it after being stored for a month, it looks terrible until it gets stretched out and then look great.
You can check out my thread:http://backyardtheater.com/forums/index.php/topic,90.0.html
BO cloth comes 54" wide, so you would need 3 strips, to get to 12' and and you would need 7 yards per strip, for a total of 21 yds. At about $6 a yard you're looking at $130. You can often find 40% off coupons. I don't know how much the canvas or vinyl you're looking at costs, but this should give you something to think about.
I'm happy to answer questions.