Abstract: A building made substantially of pre-cast components is disclosed. The building comprises of pre-cast concrete walls, floors and columns; the walls and columns being made of pre-cast concrete wall panels; and floors being made of pre-cast concrete slabs. The panels have one of ‘L’, ‘T’, cross or ‘I’ cross-sectional shapes, wherein the ‘L’, ‘T’ and cross-shaped panels are joints between ‘I’ shaped panels and slabs and panels being interlocked together to form an enclosure. At least some of the ‘L’, ‘T’ or cross-shaped or ‘I’ have a door or window opening. ‘I’ shaped panels are of varying lengths. Columns are reinforced with steel bars and additional concrete.