did the design have any kind of change?
Yes, it was later increased to 60 and then 80 stories.
Design changes
The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories. Height restrictions were placed on nearby buildings to ensure that the top fifty floors of the planned 80-story, building would have unobstructed views of the city. "The New York Times" lauded the site's proximity to mass transit, with the Brooklyn–Manhattan Transit's 34th Street station and the Hudson and Manhattan Railroad's 33rd Street terminal one block away, as well as Penn Station two blocks away and the Grand Central Terminal nine blocks away at its closest. It also praised the of proposed floor space near "one of the busiest sections in the world".

how many floors is the empire state building observation deck 3 floors. where is it located? Midtown Manhattan in New York City. what is the earlier mentioned building used for? UNANSWERABLE what kind of architecture does it follow? Pre–World War II architecture.
The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories. Yes. The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories. Yes, the original plan of the building was 50 stories, but was later increased to 60 and then 80 stories
Empire State Building Empire State Building Empire State Building
Design changes Design changes Design changes
The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories. The original plan of the building was 50 stories, but was later increased to 60 and then 80 stories.
wiki:7743535
Empire State Building [SEP] Design changes
The roof height was now , making it the tallest building in the world by far, even without the antenna. The addition of the dirigible station meant that another floor, the now-enclosed 86th floor, would have to be built below the crown; however, unlike the Chrysler's spire, the Empire State's mast would serve a practical purpose. The final plan was announced to the public on January 8, 1930, just before the start of construction. "The New York Times" reported that the spire was facing some "technical problems", but they were "no greater than might be expected under such a novel plan." By this time the blueprints for the building had gone through up to fifteen versions before they were approved.