The materials that you need is Redstone, 4 Pistons, Glass, Repeater, and a block (I suggest Wool). You need to build a Redstone Clock/Loop (Which is on one of my Blog Post). You put 4 pistons then 3 glass on each side and 1 Wool. Add one more glass that is touching the piston (Make sure you made it be in like a Square Shape). Then you put Redstone leading off of it. You put the Redstone leading to FIRST piston (With no repeaters unless needed). Then you put Redstone and repeaters to the other pistons. When you get done with all of that put a repeater going straight from the middle of the Redstone then make it go under the glass, and go back up. After that, you make it go straight with Redstone UNTIL you reach the end put a repeater next to the glass or wool. Power the Redstone Clock/Loop. Then you make it go through the wool when it goes around. Then you should be done!