Place a sign with the text [Elevator] at the top of a sign. Then place the sign at the bottom, top or in between floors. You will then able to teleport up or down. Right click the sign to go up, and shift (crouch) and right click to go down.
If you place [*] on the second line of an [Elevator] Sign, players using it will get teleported in front of the sign instead of keeping players x and z coordinates.