Lambeth Council's £68 million new civic centre moved nearer to completion in July, as the final piece of the new roof was fitted into place at a special ceremony for civic staff.
Staff added their signatures to a key steel panel before it was fixed into place at the Your New Town Hall site in Brixton.
Deputy leader of Lambeth Council, Councillor Paul McGlone, said: "I'm delighted that work on the Your New Town Hall project is progressing well and residents can already see the scale of the project taking shape.
Today's ceremony was an important step on the road to completing this project which is on time and on budget."
The project will bring staff together from the previous 14 council offices sites into two purpose-built facilities, which is estimated to save the authority approximately £4.5 million a year in running costs.
The former office spaces will be used to build over 200 new homes, which will help tackle Lambeth's housing crisis; of those homes, 47% are earmarked as affordable housing, with most available at council-level rent.
The project is being undertaken by developers Muse and Morgan Sindell, who oversaw the topping-out ceremony.
Richard Dobson, Morgan Sindall area director for London, said: "We're delighted to have reached this key point on this landmark development which will provide the people of Lambeth with a fantastic new, sustainable, user-friendly facility. We look forward to continuing to work closely with our expert project partners – including sister company Muse, and our specialist team as we enter the final phase of development."