When it opened in 1923, some questioned whether the 1,800-student Richmond Hill High School in Queens was too large. Nobody asks that question anymore. Richmond Hill has more than 3,600 pupils and could have 4,000 next fall as New York City converts other nearby high schools into mini-schools with smaller, more selective enrollments. Over the past dozen years, Richmond Hill’s most notable architectural accouterment has been the quote-unquote temporary classroom. Twenty-two of these red metal trailers, encased within chain-link fencing, occupy the school’s former yard.