Most new homes in the city today are still designed for nuclear families. According to the nonprofit Citizens Housing & Planning Council, two parents raising young children occupy only 17 percent of New York dwellings; another 9 percent house single parents with children under 25. The city meanwhile has a growing population of singles — students, young professionals, immigrants, empty-nesters and the elderly — who can’t afford market-rate rentals. (That’s not to mention a report last week from the Coalition for the Homeless, an advocacy group that has frequently clashed with the Bloomberg administration , which put the city’s homeless population at 41,204, up from 31,000 a decade ago.)