Hi there, I'm making a graduation cap cake for my friend next week and all the recipes I've seen have required me to cover cardboard in fondant for the top however I want my cake to be completely edible. Does any one else know of anything else I can use? Thank you!

If you add some tylose powder to fondant it will harden up pretty nicely. I roll it out about 1/4" thick and cut the square part and also a long strip about 3 inches tall. I wrap the strip around a soup can or a can of crisco, depending on how big you want the hat. Let both dry for a few days. Once dry you can glue the 2 pieces together with a bit of melted chocolate. Add the tassel and you will have an edible hat. Personally I don't like the taste of fondant so i wouldn't eat this! Here are some examples of a hats that I made.

nice...did you buy the silhouette or cut it out yourself?

I made a graduation cap some years ago, using a large square sugar cookie as the top.  I covered ti with butter cream.  It does need some support as it was pretty heavy even without being covered in fondant.  A good gingerbread cookie recipe would work as well. 
 

BatterUpCake, thanks I just cut them out myself.

AI used a half small ball pan for the hat base and the covered a gingerbread cookie with rolled fondant to match the tassel was fondant allow to dry resting over a flower form. Attached the cookie and tassel with royal icing