I am going to be making a cake that looks like a bottle of nail polish.  The bottle has a smaller diameter on the lower tier and larger on the upper tiers.  My thoughts were to bake a 7", 8", 9" and 10" tier (maybe 1 1/2" tall each) and stack in the same order from bottom to top.  I'm a bit worried that the upper tiers will droop and/or fall because of limited support near the edge.  Can anyone give advice and/or tricks on how to support the larger tiers as I move upward? 

With just 1/2” overhang there should be no problems.  

Your other choice is to make all the layers the same then carve it into the shape you want. 

if you want the sides a straight line smooth from top to bottom then you might wanna do two eights on the bottom so you can keep the 7" bottom diameter-- instead of using the 7x8 because that would carve out to be a 6" bottom after carving -- 

so I was wondering about the dimensions -- I went & cut out a 10" and a 7" circle out of paper and fwiw -- I put them six and seven inches apart like the cake would be and fwiw I liked it a little bit taller than 6" 

sounds like such a fun cake!

are you doing fondant or butter cream?

you could put a board in there if you want --