This will be the biggest one I've done so far so now I have a few questions.
It's going to be a 20"round x 18" sq x 14' r x 10" sq x 6" r.
All fondant. All stacked. with pearls in fondnat for borders.
I know it's going to have to go in parts for delivery. (I usually take 3 tiers as one unit) How can I Keep the bottom edges perfect so they can be stacked on site.
Just how much does a 20 " cake weigh? Am I going to need help lifting this one?
What about baking that? Do the half round pans work well? I have not used them. +each layer willhave filling too.
Any other hints are appreciated.
I can't answer any of your questions, but here's a bump. Maybe someone else will be able to help you out.
Yes, you will need help.
I don't know how to figure cubic inches on a round (never passed "pi"), but a 20" square is 1600 cubic inches of cake (20x20x4).
I made a 2-layer 28x22 once (over 2400 cubic inches .... 28x22x4) and thank GOD I had a friend/bride happen by the shop, who volunteered to go with me to deliver it because I couldn't even lift it into my van!
Measure your oven to see what pans will fit. You may have to bake four 2-layer 10" squares and cut a 20" round from it. (easy to do .... make a paper template to lay on top and use that for a pattern.
Just so you know, the diagonal (from corner to corner) of the 18" square is a little over 25 inches, so all 4 corners are going to hang over the sides of the 20" round by a little over 2-1/2 inches.
The diagonal of the 10" square is a little over 14", so all 4 corners are going hang over the sidees of the 14" round by about an eighth of an inch.
To figure out if a square cake will fit onto a round cake, multiply the length of one side by itself, then multiply that result by 2, then hit the square root button on the calculator. (Basically, you're applying the Pythagorean Theorem, the length of the hypotenuse of a triangle squared is equal to the length of leg A squared plus the length of leg B squared).
Make sure the sizes all fit properly when mixing different shapes. (I never took algebra in school, so this was a serious problem for me when I first started making those cakes!) Did the math.
A 14" square comes to 19-4/5", so will *just* fit on a 20" round with absolutely no room for error (corners will be right at the edges of the circle).
A 12" square will give you about 1-1/2" inches around the corners of the square cake, so that is the best size square to go on a 20" round.
You might need to swap the order of your tiers around and have the bottom tier be the square (can assemble by putting 4 separate 10" square cakes together, MUCH easier to do than one big cake!). So, 20" square, 16" round, 8" square, 4" round, but then that's only 338 servings...but you could always do sattelite cakes of 8" rounds with 4" squares at 32 servings each, or 8" rounds with 6" rounds at 36 servings each, or just the 8" rounds at 24 servings each.
HTH!
Thanks everyone. I think I'm going to buy the half pans and avoid all that math. I do cake--- not math. 
I use Earlene Moores cake chart for serving. this size will yeild 400. + there getting a groom cake that is a full sheet with a farm sceen to go with his john deer toy. I don't think they are having that many people she just has this one cake in mind.
I told my husband he would have to help with this one. He never has had to before. He said OK as long as I don't divorce him if he screws up. HAHAHA
What about the finish work? If it has fondant bead borders and I can't take it stacked... will I have to finish all of that when I get there. That's going tobe a lot of time getting that all done.
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