Across the nation, just 10 builders figured in roughly a quarter of all the home closings that took place in 2011, Builder magazine reports. But it also notes that in 49 of the top 50 markets—metro areas that collectively were home to 61% of the nation’s closings—more than a quarter of the closings were made by just 10 local companies. The local top 10s’ dominance of their markets ranges from 99.5% in The Villages, Fla., to 19.8% in metro New York City. The moral: If you operate in one of these markets and you don’t sell to one of that area’s top 10 builders, then you’re missing out on much of the market’s new-home business.