Don't get it done by the builder....the cost is usually close to double. I was quoted 12K for 900 sq ft (builders best upgrade option). I can get the job done for $7K (equivalent floor).
Almost everyone I know has been recommending outsourcing but I don't know a reputable floor guy and am thinking that an outsourced job would most likely not be covered by the Tarion warranty. And I've heard horror stories of leaks from improperly installed appliances damaging floors...which of course the builder replaced but those floors were installed by the builder.