The other day I was thinking about roll drops - in particular a job I bid a couple years ago that used roller shades back to back for a TV studio. The material on the shades was a print on blackout material - but they also used them for light boxes, obviously with a different material for the print.
They were using these rollers from Denny mfg. They carry 12' long drops, and are pretty economical.
While looking for the information on Denny Manufacturing I also ran across a few other companies that produce equipment that could be used in situations like these.
Titan Patio Drop Shade can do 20' wide by 18' tall