Pre engineered buildings are factory-built buildings of steel that are shipped to site and bolted together. What distinguishes them from other buildings is that the contractor also designs the building – a practice called design & build. This style of construction is ideally suited to industrial buildings and warehouses; it is cheap, very fast to erect, and can also be dismantled and moved to another site – more on that later. These structures are sometimes called ‘metal boxes’ or ‘tin sheds’ by laymen – they are essentially rectangular boxes enclosed in a skin of corrugated metal sheeting. Great speed is achieved because while the foundations and floor slab are being constructed, the beams and columns – the structural system – are being fabricated in the factory. Once the foundations and floor are done, the columns are shipped to the site, lifted into place by cranes, and bolted together.