To provide a jig for easily performing the fitting work of a runner to a rail without damaging components such as a floor, a door and a lower rail when constructing a folding door.

A guide sheet for construction is the jig used for constructing the door, comprises a thin plate whose dimension is larger than the thickness of the door, is provided with a positioning hole on the almost center of the thin plate, and has at least one mark line provided radially from the positioning hole. The positioning hole of the guide sheet for the construction is fitted and fixed to the shaft part of a lower runner, the mark line is matched with a lower rail opening, and a lower runner lower end part is fitted to the lower rail opening.