An adjustable stair stringer and railing construction assembly is disclosed. The assembly is adapted to use a pair of parallel stringer arms for each side of the stair, a riser/tread support bracket for each stair and alignment and spacing elements for spacing the support brackets along the stringers. The brackets include formations for spacing the stringers with respect to each other and for spacing adjacent brackets along the stringers. The brackets are initially pivotally attached to each of the stringers so as to be rotatably movable about their pivotal attachment as the stringers are moved axially. Axial movement of the stringers with respect to each other establishes the angle of rise of the stair. Treads and risers are attached to the brackets to form the stairs and railings are attachable to the stringer and bracket assembly to complete the construction. The parallel stringers, brackets and spacers are also used in the preparation of formwork for pouring aggregate stairs with the stringers, brackets and spacers being reusable.