In 1989, the Toronto Skydome introduced the retractable-roof, allowing fans to escape bad weather and the drab indoor environment. The flexibilty of the design also allowed many teams to return to the charm of a natural grass field. Indoor parks were built for several different reasons, chief among those weather. However, as multi-purpose parks became unfashionable, so did the drab indoor parks. This led to the creation of retractable-roof parks. These allowed shelter from the elements, but still could be opened on a nice day. To be able to support the roof, most were closed in on all sides like multi-purpose and indoor parks, but as all retractable-roof parks except Rogers Centre are baseball only, every square foot does not need to be filled with seating, and there is plenty of room for open spaces or windows that look outside. Because the roof needs to go somewhere when not covering the field, a distinguishing characteristic of the retractable roof park is a large extension of the interior spaces to either one side of the field or both sides that the roof sits on when retracted. The only exception to this is Miller Park whose fan-shaped roof folds in upon itself and hangs behind the stands down the foul lines. Often, when retracted, the roof still hangs over the field, casting large shadows. This is countered at Miller Park by large panes of glass under the roof. While most seal up when the roof is closed, other 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. The arena's long-term tenants, the NHL's Pittsburgh Penguins, never played with the roof open, and the arena itself was never used for baseball. While Montreal's Olympic Stadium was the first baseball park to have a retractable roof, the roof was plagued by numerous problems, and was never fully used. As a result, it is not generally considered to be a retractable-roof facility. This made Rogers Centre the first fully functional retractable-roof park. It managed to succeed where Olympic Stadium failed, building a multi-section roof that folded upon itself, retracting over the hotel in center field.
Retractable-roof parks can vary greatly in style, from the utilitarian (Rogers Centre), to those infused with retro elements (such as Minute Maid Park), to the contemporary (Marlins Park). The style of each park reflects the popular architecture of the era in which it was built. (This differs from indoor ballparks ? all of which were built during the time of multi-purpose parks, and thus reflected the same "flying-saucer" style.) When Rogers Centre opened in 1989, baseball was near the end of the modern and multi-purpose era. Chase Field, Safeco Field, Minute Maid Park, and Miller Park all opened in the middle of the retro era. When Marlins Park opened in 2012, it introduced a new and different style, and perhaps the beginning of a new era.