In 1938 when it opened, Gander Airport was at least 250 acres in size of graded land and it had 35 acres of paved surfaces. It's four runways used 1,230,000 square yards of concrete to complete. It was at the time the largest paved runways in the world.
Other than the 250 acres of level surface, I could find no information on the hundreds of buildings located at the airport. At one time this included a USAAF air station, which was built after the physical airport was completed, with over 100 buildings for barracks, hospitals, hangars, warehouses and somewhere in the mix a fuel depot. There was an RCAF station located at the airport as well, which had a similar number of buildings. In addition, the Royal Canadian Navy had a communications outpost that was active through the Cold War. On top of that were 1700 civilians working at the airport. It needed the infrastructure to support hundreds of flights every day to get planes to the British Isles at the height of the war.
I think the size was considerably larger than 250 acres, but there's no data at all on the physical size of the airport. After the war, the churches, schools and libraries on base were donated to the town. It has about 175 acres available for lease if you are interested.