In my experience with very large cakes it is better to bake shallow layers and stack them together. This can either be done by using sandwich cake tins or by baking shallow flat cakes and then cutting the rounds/squares from those. The problem with baking anything above a deep 12" cake is the outside areas baking so much faster than the middle. I found even with heating cores, centres take forever rendering the sides burnt or crispy. By the time the middle cooks through the cake texture is too dry. The advantages of baking in shallow or flat layers prevents dryness of the cake crumb and of course greatly reduces the time spent waiting for each cake to bake.
The layers, when stacked will still form cake dense enough to support ganache or buttercream crumbcoat and sugarpaste.
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