I've got a cake coming up that is 12" double tier, 10" double tier, 8" , 6".  The bride wants the bottom tier covered in simple gum paste flowers just like a picture from a celebrity wedding.  She wants buttercream, (I use IMBC) but I think I need to cover the double 12 with fondant, or at least with a fondant collar to hold all these flowers.  A co-worker suggested that a buttercream tier on top of a fondant one would leave a greasy stain.  Is this true?  

Btw: I'm on the coast of SC, this weekend will be in the mid 70's and its ALWAYS humid!

Fondant is not my forte.  YET!

AI've done a few projects that have bc tiers on fondant tiers, it doesn't affect the other at all, and I use SMBC. I've made a few double barrel cakes as well. I always fondant those, just because it gives a cleanerlook, in my opinion. I think it would be the best idea to use fondant if you're going to be placing go flowers around it, will be neater, no nicked bc or smudgy icing.

Thank you AZ. That helps.

I'm nervous about covering such a big tier in fondant, which is why I was considering a collar, or maybe covering it using the "paneling" method.