A structure includes a vertical support, a horizontal inner rail affixed thereto, a bracket affixed to the vertical support vertically lower than the inner rail, and a cantilever support affixed slidably-lockably to the bracket, wherein the cantilever support is affixed to the bracket in a manner that is either pivotable vertically and horizontally or fixed substantially perpendicular to the inner rail. A central rail substantially aligned with the inner rail is positioned distally from the inner rail and affixed to the cantilever support. An arch member is disposed perpendicular to the rails and is affixed to the inner rail and central rail.