A mechanism for extending a floor while erecting a structure, has a linkage, comprising a first frame element constrained proximate and translatable relative to a second frame element, from a minimum retracted length to a maximum deployed length, a third frame element having a length, and joined at one end pivotally to the first elongate frame element at an end away from the second elongate frame element, and a link joined at one end pivotally to the second elongate frame element, and at an opposite end pivotally at a point along the length of the third frame element, such that retraction of the first frame element relative to the second frame element results in the third frame element lying at an angle that is less than the angle when the first frame element is fully deployed relative to the second frame element.