Build it on the Eastern  plains--a new,self contained zero waste energy self sufficient community with small technical learning facilities attached and highways designed specially for self-driving vehicles. City central running fossil fuel free with bike paths and people movers from site to site. Lots of open land and probably some farmers who would be open to talking about selling a couple thousand acres here and there. Close to interstates, rail service.  
Express train service to/from Denver/DIA.  Amazon starts specialized training and education in local schools as soon as the deal is signed.  By the time the site opens, a trained and settled workforce is at hand. Amazon becomes the trailblazer in addressing the issues of rural kids who need a job and can't afford a four year college--and maybe want to stay in their communities.
 Jeff could be a 21st century Henry Ford--without the right wing views, I hope.
Come have a look Jeff. We'll make you a deal.