I used one cardboard cake mat although using a round cardboard cut out would work too. I hot glued a toilet paper tube to the center of the cardboard cake mat. The next part can be somewhat tricky. The pictures in the website were a great help. I did not use a cake pan. Instead I took the diapers and lined them up against the toilet paper tube then fanned them and secured with a rubber band. The picture shows a paper towel roll if your cake is going to be more than one tier.
I have seen cakes with a blanket wrapped around the tier but I chose to tie a ribbon. For the top tier I used a pack of pacifier wipes, powder and baby oil gel. I rubber banded them together and wrapped a waterproof changing mat around and secured with a ribbon. To embellish the tier I added a teddy bear book mark which was leftover from my baby shower.
Around the base of the cake I added a bib, baby toy, sleeping mask for mom, and some washcloth cupcakes. Directions for the washcloth cupcakes can be found here. I secured the cake by attaching the pieces with safety pins.
I purchased the bib, baby toy and sleep mask at the store but I would have loved to make those items myself, unfortunately at 8 months pregnant I had a hard time using my sewing machine.
For my next cake I plan to add more handmade items to really make it one of a kind.
For directions on how to use the roll method check out this website. I really like that they used a bottle of champagne for the center instead of a cardboard roll. http://alphamom.com/family-fun/activities/how-to-make-a-unique-diaper-cake-ha/