The Cty Hall building next to Tower Bridge has been completed and is being handed over to the GLA this week.
The building, designed by Lord Foster, will be officially opened by the Queen on 23 July.
According to press reports this week, last-minute alterations are being made to the main chamber.
While it is suitable for the regular meetings of the London Assembly, changes costing £140,000 are being made so it can also be used for a variety of other events.
The GLA is passing the bill is being passed to the Government Office for London because officials there originally promised that the chamber would have other uses.
Floors three to eight contain offices for staff, GLA members and the mayor.
City Hall provides 185,000 sq ft f space on ten levels to accommodate 440 staff and members. The lower ground, ground and first floors of the building will contain a cafeteria, display space and library.
The top floor of the building – described as London's Living Room – will be an open space, with spectacular views across London.