Investor Chris Hansen’s first conceptual plans were made available Friday for his basketball/hockey arena, showing a 725,000-square foot building that would be nearly double the size of KeyArena, but smaller than Portland’s Rose Garden, opened in 1995.

The designs are prototypes and not final, according to KING-TV’s reporting. Capacity at the Rose Garden for basketball is 19,980, and 18,280 for hockey. Hansen has previously said basketball capacity for the project would be a little more than 17,000.

The 386,000-square foot KeyArena, home to the Sonics until 2008 and used for basketball now by the WNBA Storm and Seattle University’s men’s program, sat 17,027 for hoops, and less than 15,000 for hockey, with more than 4,000 seats obstructed view. The Key has only 1,300 square feet for club space.

The prototypes from the Kansas City firm hired by Hansen, 360 Architecture in Kansas City, will be officially unveiled at a public meeting later this month.

The $500 million project received preliminary approval last month when Seattle Mayor Mike McGinn and King County Executive Dow Constantine signed an amended memorandum of understanding for the public-private deal that includes a $200 million lease-purchase agreement with the governments, once the project passes a state-mandated environmental review that includes consideration of locations besides SoDo, Hansen’s preferred choice.