Hello!
I have a question, Its my first time working with fondant, and I want to know if I can refrigerate  my cake cover with fondant or should I just leave it outside.The cake is going be filled with Chocolate ganache. I don't know if that would affect of leaving the cake outside or in the fridge. (Where I live its like 85% humidity :/ ) 
I'm making the cake for my sister birthday that is on Saturday, and I want to make the cake on Friday.

Thanks in advance for you help :D

Yes you can refrigerate it.  Just wrap the box with plastic wrap and when you pull it out to let it come down to room temperature, leave the wrap on so condensation develops on the wrap, not the cake.