Kevin Walter made this absolutely amazing LEGO Barad-Dûr for Brickworld 2011. I’d be curious to know how many pieces he used to make the tower, but the only details I got from his Flickr account is that the construction measures 175cm tall. In case you want to see more pictures, we’ve added a bunch of other ones in the picture gallery below.
Then at last his gaze was held: wall upon wall, battlement upon battlement, black, immeasurably strong, mountain of iron, gate of steel, tower of adamant, he saw it: Barad-dûr, Fortress of Sauron. All hope left him. Source: The Fellowship of the Ring, page 521.