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.The structural system of pre-engineered steel buildings give it its speed and flexibility. This system consists of factory-fabricated and factory-painted steel column and beam segments that are simply bolted together at site. The columns and beams are custom-fabricated I-section members that have an end plate with holes for bolting at both ends.These are made by cutting steel plates of the desired thickness, and welding them together to make I sections.