According to the official website of Wembley Stadium:For the majority of event days at Wembley Stadium, the roof is in its fully closed position - lined up with the touchlines leaving the seats covered but the pitch uncovered.
This is how Wembley Stadium has been designed as it allows for the playing surface to receive maximum sunlight. Wembley Stadium does not move the sliding roof whilst visitors are in the Stadium.
In the event of heavy rain some visitors on Level 1 can get wet, so we would recommend visitors dress accordingly.
As Wembley Stadium's roof does not close fully, visitors with tickets for the standing pitch area at concerts will get wet in the event of rain.
See the Related Link to the official website of the stadium.