Work has started on the Buro Happold-designed roof of the British Museum's Great Court. Circling the famous Reading Room, the roof will create the largest covered square in Europe. Construction of the roof is complicated by the fact that the Reading Room was built off centre within the two acre courtyard. The construction process begins with 152 ladder roof sections being lifted by crane over the museum onto a 20m high platform covering the entire courtyard. The ladders are then joined to form a triangular-patterned lattice structure which is attached to the supporting steelwork.