I've been asked to make a cake for a high school play set piece.  They want it on the large side and whimsical.  It is for Alice in Wonderland. 

How do I make a fake cake?  Do I just cover styrofoam with fondant?  Buttercream under the fondant?

Where do I find styrofoam in cake shapes?

It will also need to be durable since it will be used many times and moved around a lot.

Thanks!

You can get the cake dummies from  this company. they are reasonably price and they don't charge a lot for shipping  http://www.dallas-foam.com/store/cakedummies.html

And here's a link on how to cover the dummies.

You can google Cake Dummy. It will come up with different results for styrofoam cakes. Good Luck :)

Wow!  You guys are awesome!  Thanks for the info!
 

You're welcome good luck : )

Since it won't be seen close up, needs to be durable and will never be eaten, I would look into using spackle, caulk, etc for it. 

http://www.jerriblank.com/amy_ready-made.html/

http://www.ehow.com/how_10022180_pipe-spackle-decorating-cake.html 

I just googled permanent cake out of spackle and these are two of the links that showed up.  Instead of cake dummies could you use round hat boxes or round paper mache things from Michaels, Hobby Lobby?  Not sure if it would be cheaper but might be.  Then you could just paint it in craft paints for the bright colors for your Wonderland cake theme.