I want to make a seperated topsy turvy cake and need some help figuring the stability of the cake.  I know most topsy turvy cakes are covered in fondant can you make on in buttercream and will it stay?  How long can you leave this displayed before gravity takes over?  I'm thinking of using this for a wedding cake and it would probably be on display for at least 8 hours before it is served.  Any help or pointers would be appreciated.  Thanks,

Do you have a picture of the construction you are trying to achieve? 

Also, what type of cake/filling are you planning on using?

I want to do something like this in buttercream.  WASC with buttercream filling.  Gumpaste flowers
 

Wow!  Gorgeous.   Does it have to sit out for 8 hours?   That is a long, long time.   As smooth as I can ice a cake...after one of my wedding cakes sat out for about 6 hours, bulges started to occur.   That was just too long to sit out.  

Yes it probably would sit that long as i am the MOB so I would have to deliver the cake early.  I'm thinking around noon as the reception starts at 5:00. 
 

As a former MOB who made her DD wedding cake(s) I have to say this.  I'm a professional, decades of experience, I had delivery help.  DO NOT ruin your experience with your DD's wedding with this amount of work.  I got 5 hours of sleep total in the three days before the wedding.,  So not worth it.

I know I can do this. I've done it before as a MOB twice, just not a topsy turvy.
 

Wow that's a monster! If I were tackling this, since you can't actually see the gaps between the separated tiers (as they're filled with flowers) I'd carve the tiers to look topsy-turvy but stack them level, that way you're not actually tilting any cake and it should lengthen the time you can leave it sitting without problems, but unless you can sneak in a heavy ganache dam perhaps, I agree that you'll see bulging by the end of the day.

I tried to do a quick sketch of what I mean- red outlines the cake and green to show the BC layers- it should just show lots of flat level layers even though the finished tier looks slanted- this method helps stop sideways slippage.

...think carefully about splitting up the design for transport though

Thanks for the info.  I like your idea.  I'm using Styrofoam separators in between each tier.  The styrofoam will serve two purposes, strength and stability for the cake plus I can secure the flowers in the styrofoam.
 

AMy suggestion would also be styrofoam. What about bringing the cake to the venue "frozen", or close to. Then stacking at 3 or 4pm?

Thanks.  I really like the idea of stacking it around 3:00 - 4:00 - that might work.  Thanks for that info I never really gave that a thought.  The wedding isn't until August so I have lots of time but I like to get things figured out so I can try and be ahead of the game.  Lots of flowers to make in the meantime.