Abstract: The invention relates to a lightweight concrete building structure using pre-stressed lightweight structural beams 46 with a lightweight floor panel (48) spanning between beams (46). In a particular arrangement, the parking system using building structure (10) may be about less than half the weight than traditional parking building structures. In accordance with one arrangement of the particular embodiment of the invention, the building structure comprises floor structures having one or more structural beams, and one of more lightweight panels for attachment to the structural beam, wherein the floor structure is defined by joining together the one or more lightweight structural beams and the one of more lightweight panels. This particular arrangement is particularly useful because it permits defining a floor structure capable of sustaining relative large loads (such as a multitude of vehicles) using lightweight floor panels.