It took four years to build the Royal Albert Hall. While the building itself was being constructed in London, the roof was built in Manchester. It was taken to pieces for its journey by train to the capital, then put together again on arrival.
The roof simply sits on top – it is not attached to the Hall building in any way. When it was put in place, the weight of the roof caused the Hall to sink by just under a millimetre. It remains a sturdy construction after 150 years – the roof of the Royal Albert Hall is able to withstand the weight of up to 158 tonnes of snow on a particularly wintery day.