 It cost, complete with fittings, nearly £35,000 to build.The main feature of the building is the lofty fireproof central repository, the Dome, which consists of five tiers of ironwork shelving and galleries and is surrounded on the outside by staff and search rooms on three floors.The Dome is a large and striking circular chamber, over 27 m (90 ft) high and of interest as a piece of 19th century functional architecture and structural engineering.