A marquee is a roof mounted flat panel that makes the trailer appear to be taller than it is, similar to a false front on a store building. The main uses for marquees are for signage or to provide a higher attaching point for awnings, if needed.
The marquee can be folded down during transport to avoid height problems. It can be either manually or electrically actuated to fold up or down. Manual is the most simple and most reliable but requires that someone go up on the roof to do it. That in turn means the roof must have a place to walk on as well as ladder access to it. If the access is from inside the trailer a trap door in the roof will be needed. If electrically actuated, the trailer's roof will have to be lower so the height of the mechanism will not be over height or the mechanism will have to be mounted in a depression in the roof so the top of the mechanism is flush with the top of the roof.