For photographic purposes, the best idea would be to put the logo as high as possible on it. The reason? When photos are being taken, if there is a person in front of the roll-up, the brand will be covered. Put the logo very high on the banner.
Note: Tip via Radu Grozescu.
Note: Also see the Yahoo! Group on which I present similar issues: IMRo. To join, email email@example.com and reply to the confirmation email.