A system for constructing a tank is made up of a plurality of generally rectangular prism sections, which are hinged together on the back side to form a platform, having an end section hinged to a frame section, a cantilever frame extending from the end section, a counterbalance frame attached to the cantilever and extending parallel to the platform and opposed to the end section, with the end section and the counterbalance frame being separated by a pair of saddle wheels mounted to the cantilever frame. At least one additional saddle wheel is mounted on a frame section for cooperative operation with saddle wheels on the cantilever to support the system on the tank wall and to move the platform within the tank wall as it is constructed. The hinge connections between the sections allow the platform to be adjusted to the arc of the internal wall of the tank under construction.