The £27 million project, designed with London-based architect Philip Gumuchdjian, will create 12,000m 2of new space for the gallery in the Franco-German border town.
The Metz gallery was originally expected to open next year, to coincide with the 30th anniversary of Richard Rogers' and Renzo Piano's Pompidou Centre in Paris, but it is understood that it will not welcome its first visitors until late 2008.
The large pavilion will sit in a new park within Metz's Amphitheatre district and will boast an unusual 'giant hexagonal' woven steel and plywood roof, inspired by a woven bamboo Chinese hat found by Ban in a Paris market.
The building will house exhibition halls, studios, conference rooms and administrative offices.
Ban, who has set up a studio on top of the original Pompidou Centre to manage the project, beat more than 153 international entries to win the competition almost three years ago.
Among the losing finalists were Herzog & de Meuron, Dominque Perrault and London-based hotshot Foreign Office Architects.