After 20 months of hammering, drilling, cladding and building, the new Colston Hall foyer is finally finished.

Work on the development is over, and the hall's staff have officially taken ownership of it.

Now the bars and cafes will be fitted out and the foyer prepared for its public opening in September.

But people can get a sneak preview at an open day on May 16.

The £20-million project, which was funded by Bristol City Council and the Arts Council, was completed on time and on budget by contractors Willmott Dixon.

The golden copper-clad building in Colston Street boasts five floors, a glass front and a wind turbine on the roof.

Inside the airy building there are two bars, a new ticket office, cafes, rehearsal rooms, performance spaces, workshops and studios, as well as a walkway through into the main hall.

Art – including a collection of 3,500 badges of rock and pop stars arranged into a constellation – are being installed later on this month, and staff move in properly in early May.

Graeme Howell, director of the Colston Hall, is delighted with the finished article.

He said: "I have had a countdown timer on my computer since work started, and now it has finally stopped.

"We started construction 88 weeks ago, and it is funny to think it is finally all done.

"It has been a real talking point, and has given a really different aspect to the city. You come into the city centre and see this big copper cladding and it says, 'Hello, welcome to Bristol'.

"One of the things I love about it is that it is a contemporary structure set against the beauty of the Colston Hall. It is the modern linking with the past, which is a real reflection of Bristol."

The hall has maintained a full programme of acts and concerts throughout the work, which Mr Howell puts down to the dedication and hard work of the staff.

He said: "I has been five years of my life, working on this, and I am proud of the amazing team of people who have brought this together.

"It is a proper, 21st-century concert hall, something Bristol has been trying to achieve for a long time.

"But it is also a real focal point for the music industry in the city, which is an important part of Bristol.

"What it really does is become another key part of the jigsaw of Bristol being a really great city in the 21st century."

More than 1,000 people have worked on the development since building started in July 2007, when the old Colston House was demolished.

By May last year the concrete frame of the foyer was complete, and the walkways between the new and old buildings were in place.

Waterproofing of the roof was finished in August, and the distinctive copper cladding was completed in October.

By the end of today, 95 per cent of the construction engineers will have gone, with just a handful left to finish Tarmacing, paving and putting up signs.

Willmott Dixon's operations manager, Richard Jones, said: "It has been a really great project. It has been a very positive project. The quality is very good, and we are all very proud of it ."

Simon Cook, the council's executive member for culture, sport and tourism, said the new foyer would be a real boon to the city centre.

He said: "It looks fantastic inside, and it is a beautiful state-of-the-art building.

"It is very different to what is around it, and that makes it a landmark in Bristol.

"The wonderful recycled copper finish has a golden quality when the sun shines, and the high-quality finish sets the tone for what we want to do with the rest of the building. There is a performance space inside that will be open all day and evening, and this will really change the culture of the Colston Hall.

"It has a real feeling of vibrancy, and will bring a life to the hall that we haven't had before. That, I think, is a real step forward."

Staff are now working with the council to secure a further £40m of funding to transform other parts of the building.

This second phase of development will be split into two parts. One part will see the development of the historic front of house and box office area, and the other will see a refurbishment of the concert building, including the stage, the backstage area, the roof, air conditioning and the conversion of the current bar into a second hall.

Digital studios are also planned, and gala-style seating could be installed, allowing for seats to be cleared away completely for rock concerts.

Funding could come from the Arts Council, the Regional Development Agency or the Government.

- Breakout: The new foyer, floor by floor:

Ground Floor: On the Colston Street entrance level there is a new cafe bar, a foyer performance space, a shopping area, first aid room, toilets and lifts

First Floor: The Trenchard Street entrance, this floor has four new educational facilities, a bistro restaurant, the box office, cloakrooms and merchandising space

Second Floor: Level with the Colston Hall's auditorium, there is bridge access into the old building, and the first of the new interval bars

Third Floor: Has the entrance to the hall's balcony, and office spaces

Fourth Floor: Bridges leading into the back of the balcony mean wheelchair customers can access the balcony for the first time. There is also the balcony bar, with fantastic views over the city.