I just saw this project posted and remembered i made a diaper cake too for a coworker late last year for her baby shower.
This is a cute and unique way to give a practical gift. I know expectant moms will find this adorable but very usefull.
Start off with about 2 packs of diapers...the type with disney characters or any other cartoon or desing will work great because it will give it a splash of color so that its not just a plain diaper with colorful ribbons.
Take each diaper and roll it up. Use rubberbands to keep it rolled. as soon as you have enough (about 25 diapers) put them together standing up and hold them together with a bigger rubberband...(dont worry about the rubberbands they'll get covered later on.)
Keep making these bases each time making the next one a bit smaller than the last one...It's your choice how big you want to make each base and how many towers you want to make the cake...when you're done just stack each tower on top of each other (from biggest on bottom to smallest on top
Next you want to use a thin piece of plastic tubbing (preferrably white so it wont be visible) and stick it in the middle of your diaper cake...this will help keep the diaper cake from falling apart.
Using decorative ribbon wrap pieces around each tower to both cover the rubberbands and to decorate the cake...If possible you can use whatever color is being used for the theme of the baby shower or pink, purples and girly colors if the baby will be a girl or blues and greens if the baby will be a boy...BE CREATIVE!!!
Lastly, you want to use baby toys or any other cute items you wish to decorate the top and or sides of your cake...again be creative!