A football stadium.
My buddy made a pyramid! Huge, too, all the way to the limit of the sky. It's fairly easy: just find the sky limit, count how high it is and calculate how big it'll be on a side! It's epic, and fun, too!
make a giant sign that says "moobeat rules"
http://www.minecraftwiki.net/wiki/Minecraft_Wiki^ That place will have everything you'll ever need!