Olympic Stadium officials say a new, bigger roof will be built for $63 million.
The E20 Stadium Partnership, which manages the site, says the new roof will turn the stadium into a multi-use venue.
Dismantling the existing roof will start later this year. The new one will be twice as big and cover every seat.
The new roof is expected to be completed by spring 2015, in time for the rugby World Cup. Other work to transform the stadium will be finished so West Ham can use it for its 2016-17 soccer season.