I need to do the buttercream swirl roses on a wedding cake.   All of my cakes are assembled on site, so I'm trying to decide if I just have to pipe all the roses after set up.  I don't see how to drop the upper tiers without smashing all the previous roses.  I use IMBC, so they will be firm, but will likely break off in chunks.  Do most people transport cakes fully assembled?  Often I don't have access to the cake stand until I arrive at the venue.   

thanks for any advice!

It depends on the cake, but I usually transport my cakes partially assembled.  For example, I transport a 4 tier cake in two parts - bottom two tiers stacked and top two tiers stacked. I stack the two parts at the venue, finish the decorations, borders, etc., where they are stacked and I'm done.  Even if you don't have access to the cake stand, you have your bottom tier a cake board, right?  And your imbc roses will work fine made ahead of time and chilled or even frozen til you go to your venue.  They will thaw pretty rapidly though so I hope you don't have far to go.  A small cooler with a chill pack in the bottom could be helpful for keeping them cold til you arrive and need them.  

If it was me I would do the swirls (you mean the rose swirl rosettes, right?) on the sides of the cakes ahead of time.  Transport, assemble, then do the rosettes on top of the cakes.

I agree, do all of the work ahead of time and deliver assembled.  I made a 3 tier cake covered with buttercream rosettes amd delivered with no problem at all.

Thank you for all the input!

Yes, denetteb, I do mean the swirl rosettes.  I think I will do the sides and pipe the top on location.  It's good to have a plan.