the girls at work freeze the cakes all the time.
they base them while frozen. they said it is better to work with them frozen, and the larger cakes dont crack as easy when frozen.
some are preped with icing, frozen, then later decorated, and some are decorated all the way then frozen. but they dont recover the cake with icing after they pull it out of the freezer, only decorate it.
Ok so if understand sorry for my poor english!
I do my cake and recover it with buttercream and i can put on freezer with decoration or not ?? or i can just put buttercream and after i do my decoration.
And marzipan it's ok ??? can i put royal icing on it ?? it's ok for freezing??
Thank you for your help 
you can use what ever you want to decorate. it will come out fine.
just remember that if you cover it then freeze it, thats ok. but dont cover it again, only decorate it. what will happen if you try to rebase the cake, is the first coat of icing will lift up. so if you feel that a part of your cake needs to be "fixed", add a decoration, or try to cover it with some piping and smooth out very carefully. other than that you should be fine. and if you want to decorate and refreeze, then later add more decorations that is ok too. hope that helps.
The top cake of my wedding cake was frozen. When taken out of the freezer (one year later), it looked the same. It still tasted great too. It was covered in plastic wrap, foil, and a plastic wrap. We just unwrapped it before thawing so the icing would not stick.
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