oh no use half-sies. get two or one bowl shaped cake pans.. don't use the whole dome.
do as you would do making a normal cake, of the type you're doing.. if you have pudding in it or it's a certain type of cake mix...
but use two or one bowl shaped bowl or cake pan... and then when it's done, harded a little in the freezer (or use mayo or better yet.. a bit of miracle whip (it acts like cement, hardens the cake enough so you can shape it using sharp objects)
and when the cake halfs have cooled enough, cut to shape then make one half so it will support the other half and then put the two halves together.. then make sure your icning or other additives you're using will keep them stuck together.
if you do it the other way you'll be fussing all day trying to keep it from burning.
chefs do it all the time.. taking a million pieces of a cake and making it into a huge object.
just make sure your cake isn't too tender.. the unfortunate outcome with fancy shaped cakes it they're not tender kinda tough and dry. but you got to compensate for the idea.
you may want to get enough stuff just in case the first try is a failure.
good luck.
oh you may have to compensate additives like the egg... i'm unsure it if lesser eggs make a tougher cake or more eggs makes a cake firmer?
you may want to check up on google.com for "making a designer cake" or "how to create a designer cake" cake design recipes so on something in that general catagory