Meredith Giuliani always fantasized about saying “I do” on a grand scale. So, hosting her over-the-top nuptials in Grand Central Terminal was nothing short of a splashy dream come true. “We just thought, ‘How cool would it be to turn one of New York’s most stunningly beautiful landmarks into a main character at our wedding?’” Giuliani, 32, an Upper West Side transplant from New Jersey, told The Post, joking that the transit hub acted as the architectural “best man” for the fête.