A multi-floor building construction system for progressively constructing floors on loadbearing means of a foundation as the occupational need to do so arises and while subfloors can be occupied, said system comprising a permanent roof structure of any desired architectural shape: said permanent roof structure is displaceably supported over an uppermost floor of at least an upper one of one or more existing occupational floor space over said foundation, extensible load support means secured in said permanent roof structure until the completion of the multi-floor building, said extensible load support means resting upon said uppermost floor to support a total load of said permanent roof structure, said extensible load support means being extendible downwardly to push against said uppermost floor to raise said permanent roof structure, means to operate said extensible load support means in synchronization to elevate said permanent roof structure to create a construction zone over said uppermost floor of the building structure where an occupational floor space is to be constructed under said permanent roof structure with said permanent roof structure held elevated from said uppermost floor by said extensible load support means, characterised in that means to transport construction materials within dedicated and enclosed spaces isolated from said existing occupational floor spaces, and occupant services providing means adaptable to said occupational floor space to be constructed and integrated with existing occupational floor spaces, and adjustable hoisting means secured inside said permanent roof structure for connection to construction subassemblies prefabricated in said construction zone, said extensible load support means lifting the construction subassemblies connected to the adjustable hoisting means while simultaneously raising said permanent roof structure. said permanent roof structure is displaceably supported over an uppermost floor of at least an upper one of one or more existing occupational floor space over said foundation, extensible load support means secured in said permanent roof structure until the completion of the multi-floor building, said extensible load support means resting upon said uppermost floor to support a total load of said permanent roof structure, said extensible load support means being extendible downwardly to push against said uppermost floor to raise said permanent roof structure, means to operate said extensible load support means in synchronization to elevate said permanent roof structure to create a construction zone over said uppermost floor of the building structure where an occupational floor space is to be constructed under said permanent roof structure with said permanent roof structure held elevated from said uppermost floor by said extensible load support means, characterised in that means to transport construction materials within dedicated and enclosed spaces isolated from said existing occupational floor spaces, and occupant services providing means adaptable to said occupational floor space to be constructed and integrated with existing occupational floor spaces, and adjustable hoisting means secured inside said permanent roof structure for connection to construction subassemblies prefabricated in said construction zone, said extensible load support means lifting the construction subassemblies connected to the adjustable hoisting means while simultaneously raising said permanent roof structure.