Instructions
Change the settings of the game so that you begin with an empty screen at level one, the slowest level of game play. This will give you more time to design shapes without worrying about losing the game.
Stack tetrads into a wide tower in the middle of the screen, rotating them using the arrow keys for the best fit. Keep the sides of the tower smooth, with no protrusions or indentations. Leave a few columns on either side of the screen empty, to keep the game from subtracting lines, so that it maintains a clean tower shape.
Allow a few small gaps in the body of the tower, to create windows. Ideally these should be one square wide and two squares tall, but this construction may be impossible depending on the types of tetrads that are falling at the moment.
Begin making the tower wider when it reaches the halfway point on the screen. Increase its width by one or two squares on either side and give it a couple more rows of height. Create the crenellations of the tower's battlements, leaving vertical gaps in the top of the tower for archers to shoot through. Continue until the solid sections, known as merlons, are three or four squares high.
Pause the game to view your handiwork. In the classic Microsoft version of "Tetris," press the F3 key to pause; if you are using a different version of the game, consult your documentation for details as the pause key may be different.