PURPOSE: To provide an optional dome space and an optional outer peripheral part of ready-made unit rings by arranging a large number of the unit rings with curved face plates set on central through hole parts of ring parts on a dome roof face and simultaneously joining the ring parts of the adjacent unit rings with each other.

CONSTITUTION: By arranging a curved face plate 3 on a circular or polygonal through hole part provided in the center of a ring part 1, a unit ring A is formed. Thereafter, this unit ring A is arranged on a dome roof face. Thereafter, it is joined through a joint part consisting of a mortice type U bolt and others provided on the ring part 1 of the adjacent ring A. Thereafter, in a circular arc recessed curved face space of four pieces of the adjacent unit rings A, a circular plate 6 is fit. Consequently, by constructing a dome roof by way of combining the ready-made unit rings A, it is possible to improve workability and working precision.