The first step is to wrap all the diapers with rubber bands. I've heard you can skip this step, but it is harder for the diapers to stay rolled. The color of the bands doesn't matter as they'll be hidden by ribbon.
The next step is is to make the bottom layer around another gift item, such as baby lotion. Secure your layer in place with a big band.
Repeat this step to make the second layer.
Adding an "It's a Boy" lollipop and cute elephant for the cake topper. And tying ribbons around the layers to hide the rubber bands.