How do i make a sonic screwdriver?

Ok so i like well love to watch doctor who, and i really want a sonic screwdriver, but i dont have enough money to buy the awsome replica, so i want to make one. I know how to make one i just cant figure out how to get the right tubing for it, also how big it should be. So if you guys could, could you help me and put in some stuff to help me with this project? And so how do i build a sonic screwdriver?