New York dance companies are in a building boom. Alvin Ailey and Trisha Brown are both building new homes, and Mark Morris built one last year. “It speaks to their ability to reach an audience that they are stable enough to afford their own homes. There’s a moment in the development of nonprofits where they institutionalize. It’s wonderful to know where your next rehearsal space is and what kind of amenities—showers and lockers—you’re going to have.”