Symphony of the Seas and her sister Harmony of the Seas
were built at STX France. They are slightly larger than the near-sisters Allure of the Seas and Oasis of the Seas built at Turku. A brief description of Symphony of the Seas is found at wikipedia. Cruisetricks.de offers a plethora of information on the Oasis Class, you can also buy a German travelguide on the Oasis class ships.
A noteworthy special feature of the Oasis class ships is the split superstructure inspired by concepts from the early 1980ies; e.g. read the following two articles:
A first implementation of such a split superstructure was seen aboard the ferries Sija Serenade and Silja Symphony built in the 1990ies. However, Oasis of the Seas is the first ships where this area is not an interior space but an outdoor area resembling a park like ambience. The artist Hung-Chih Peng based on of his projects on the design of Oasis Class - read this article about the project 'The Deluge: Noah's Ark'.