LEGO 628 Extra Large Grey Building Baseplate Build your own house on the LEGO Extra Large Grey Building Baseplate! It's the big, basic piece you need to build just about anything. 15-inch square base with 48 x 48 studs for maximum building fun! There's no better place to start building! This grey baseplate is 15-inches square, so it's a great place to build homes, castles, skyscrapers, or what ever your imagination comes up with.