I wouldn't know, but it can't be too tall becuase in the book, saruman looks down from his balcony thing and talks to Gandalf, that is the same balcony that he talks to the orcs from, and then there is atleast 200-300 more feet above the balcony, and the balcony has to be in earshot of the ground, so your might be looking at 250- 350 feet