An eight-year project to repair the corroded, leaky roof of the landmark Council House will be completed in a bid to win £5 million Lottery funding for a new history of Birmingham exhibition.

The council has been fixing the Council House extension roof since 2001, and has approved an extra £1.5 million towards the sixth and final phase of repair work including the restoration of architectural features destroyed in Second World War bombing raids. The total cost will be about £11 million in eight years.

The council cabinet has also backed using this spending to support, through match funding, a £4.9 million Heritage Lottery Fund bid towards the new city history exhibition at the Birmingham Museum and Art Gallery.

The Birmingham History Gallery will cover the city’s development from foundation, through the Industrial Revolution to 1945 – putting an additional 2,000 items on display.

City culture chief Coun Martin Mullaney (Lib Dem, Moseley and Kings Heath) said: “This exciting project will further enhance and improve a world-class museum here in the heart of Birmingham, telling the tale of our great city from medieval times right up to the 20th century. The aim is to raise the profile of Birmingham as a city with a nationally and indeed internationally significant heritage.”

The Gallery will have historic exhibits from the city’s industrial past – in storage at the museum’s Collection Centre in Aston – on permanent public display.

The Heritage Lottery Fund is expected to decide on the bid by November. If all approvals are given, building work will begin in autumn 2010 and the exhibition will open in September 2012.