Beautiful Cake!! I wouldn't have the first clue of where to start. The only thing I can think of would be fondant rolled out thin and put on to some kind of egg crate to make wavy? I'm sure there is a different way!
I've seen this cake before and it's just stunning. Seems like I read somewhere how she did it but for the life of me now I can't remember. If it comes to me I'll repost.
i attempted to do something similar several months ago.
My suggestion is to use a gp/fondant mix and roll it really thin. Then I used paper crumpled up to put under the fondant to create the waves as it dried.
Mine turned out okay but not great as I used straight fondant and did not roll it near as thin as needed. It was okay for a first try.
After the waves dried I placed them between the tiers of cake.
HTH a little! I am sure your cake will be fabulous, you do great work!
I too was thinking about thin gumpaste/fondant mixture laid on top of something the make the waves.
Newmansmom-if it does come to you, please let me know. I just love this cake.
I'm just giving myself a bump, incase anyone else has some ideas.
Here is the link to a thread that was a while back. It explains how she did it. http://forum.cakecentral.com/cake-decorating-ftopict-45216.html
Holly, thank you. That is perfect!!!