The nation’s third-largest apartment developer, Wood Partners, is back in the game after the housing boom, and is working on 996 units in Miami-Dade and Broward counties. It plans to build an additional 1,500 apartments in the next 18 months. The collapse of condo developers has widened the competitive field, although financing remains a challenge. Jay Jacobson, the company’s partner in charge of Wood Partners’ South Florida division, said he started quietly assembling land and rezoning it for apartments around 2006. Once home sales began slowing and construction prices dropped, he said it was the right time to jump in again.