I made a birthday cake table runner awhile ago (sigh, that's a UFO... I forgot about it) where it was just a rectangle with a smaller rectangle on top. I then was supposed to embellish with ribbon and schtuff to make it look all cake like. I think the table runner had a pedestol for the cake to sit on, where it was a long thin rectangle with a more square like one below it. I just remember it being very simple to make.