Set up a box for the paddles
I set up a box that controlled the paddles. Both are controlled at the same time from one button using a series of gears running from the servo motor. Using an uneven amount of gears I was able to make the two paddles spin in an opposite direction at the same time. Both paddles are using the large technic gear with four smaller gears between them. I connected the bottom of the servo to two technic shafts so that it could be connected to a technic beam when installed in the box.
Gear Box - there are enough gears to make the opposite side rotate a different direction. The servo motor is on the right (gear removed to show servo underneath)
Lego on the Servo (Sorry for the blur)
Set up a mechanism to send the ball up to the top of the board
I tried several different ways of doing this and ended up going with a rubber band through a technic beam. This combined with lego slope blocks to create a ramp worked pretty well. Almost too well I then needed to create a tunnel for the marble so that it wouldn't shoot right off the board.
Build a board for the ball to play on
I connected a lot of different base plates of various sizes then topped everything with smooth lego pieces for the marble to roll on. You could leave open area's for the ball to fall through or to run lights or motors through. Connect the board to the paddle box using a hinge piece or several hinge pieces. If the board doesn't want to stay sloped you could use slope blocks along the side walls of the build to keep the board in place.
Conglomeration of plates on the left (underside of the board), some inner working on the right (dc motor and long leds)
Here is the little bits layout under the hood.
The power supply in the back goes to a fork in the main chamber via a wire. The fork has two long leds on one side and the DC motor in the center with another wire connected to it. The wire from the DC motor goes to a button that is connected to the servo that runs the paddles.