Uli Sigg, who is believed to have the largest collection of Chinese contemporary art in the world, is negotiating with the Chinese government about donating a large portion of his collection to build a museum in China, possibly in the city of Shenzhen, according to art insiders. A few years ago, the creators of the Estella Collection had tried to sell that collection to China to become part of a museum. They later decided to auction the works at Sotheby's.