 While most stadiums seal up when the roof is closed, others are at least partially open, with large gaps that do not let in harsh weather, but don't give the feel of being inside.Except for Rogers Centre, all of these parks feature natural grass.Pittsburgh's Civic Arena was the first sports building in the world with a retractable roof; however, the building was originally constructed for the Pittsburgh Civic Light Opera, which moved out in 1969 due to dissatisfaction with the acoustics in the arena.