A friend has asked me to make the AIW unbirthday cake for her granddaughter. Ive watched tutorials on Topsy Turvy cakes but this doesn't really fit that description. More of an upside down cake. Bigger on top than on the bottom. Please, just some simple suggestions on how to make sure it stands up and how to frost such an unstable cake. I'm sure I'll have to shave it down to that shape, but what should I start with? It's to be small, just a smash cake. Thank you so much for any help!  Oh, and she doesn't want fondant.

Based on what I have seen on tv cake shows I suggest making the cake exactly as you would a regular on - ice each tier one at a time, then stack, then you just turn it upside down.  In my opinion you need a dowel (or plastic pipe) bolted to the board and push the cake onto it.  Hope you understand how I discribe this. 

OOOOPPPs just re-read the 'whole' post and realized this is just a smash cake so I would use a 6"round , shave down another one to about 4" (or, of course if you have a 4" pan just baked in it) then top those tiers with a cupcake.  Make super sure that cupcake is *flat* and possibly a jumbo one.  Again, I'd ice each tier, stack then invert. 

It's been a while since I've seen Alice in Wonderland, but I was obsessed with it as a child, so I remember the cake quite well :) I would just do a small tapered tier. Wicked Goodies has a good tutorial:

http://www.wickedgoodies.net/2012/07/how-to-taper-cake-tiers/