When Aaron and Anna Schiller began thinking about building a new home in Brooklyn where they could start a family, Mr. Schiller knew he could use his training as an architect to his advantage. It was 2017, and housing prices were already soaring. Mr. Schiller, 39, the founder of the architecture firm Schiller Projects, assumed the couple would buy something “that was relatively unattractive to the rest of the market,” so they could get a good deal. But he had another agenda. “I was seeking an opportunity to do something I couldn’t find a client to do at that point…
