A support structure for suspending a window washer from the top of a building is disclosed. The support structure includes a counterweight carriage, a center support, a beam affixed to the counterweight carriage and the center support, and means for suspending the window washer from the outward end of the beam. The counterweight carriage has a frame member, a ballast container, and at least three wheels that allow the counterweight carriage to roll along the roof. The counterweight carriage further includes a steering mechanism to facilitate moving the carriage and support structure around on the roof.