If the arena is included with the Seattle skyline, there's no need to worry about trademark or architectural copyright.  I couldn't find any information about the building itself being trademarked, which would only matter if the photo's primary subject is the arena.  However, I did read that the arena is owned by the City of Seattle, thereby making it public property. 

I also searched the US Trademark Electronic Search System, and found the single word "KEYARENA", in a typed drawing, is trademarked by KeyCorp Corporation, a sports facility company in Cleveland, Ohio.

A long-winded note about images containing trademarked or copyrighted primary subjects: US law allows photographers to shoot trademarked or copyrighted works and license the photographs without penalty.  The onus falls on the buyers / end-users of our images to prove whether or not they have permission to use an image depicting a trademarked or copyrighted work. 

For example, I can shoot and sell stock images of Coke cans with the Coca-Cola logo emblazoned on the front to my heart's delight.  On the other hand, the buyers / end-users of those images MUST either 1) use them for editorial or artistic purposes only, or 2) for commercial usages, have a written agreement in place with the trademark or copyright owner to use images of their work.  A restaurant with an agreement to sell and promote Pepsi would not be able to use my photos of Coke cans to promote their restaurant, but a restaurant with an agreement with Coke can (no pun intended).  The same goes for my own business.  I can't use my photos of Coke cans without a commercial agreement with Coca-Cola saying I have their permission to use my images of their product to advertise my photography business.

Fortunately there is a loophole built into the law that allows photographers and agencies, for sales purposes, to publish individual photos contained within our portfolios.  Just can't use them for advertising purposes.

So...with that said, you are free to shoot the Key Arena however you want to shoot it.  Your main decision is how to and whom to best distribute your photos for licensing purposes.  Wide angle shots can go RF and micro, while close-up shots need to go RM, because they are more willing to accept what I call "outtakes"...aka great shots that will only sell once in a while for bigger bucks.

Thank you all for the in detail - I thought the city of Seattle does own the arena thus good to good as long as I don't isolate the building. Just like the space needle you cannot isolate it to sell as RF. T