AI'm fairly new in the cake decorating world and I've been using marshmallow fondant with buttercream because it tastes better, however, if I don't keep the cakes in the fridge it gets really soft and sometimes droopy. Is there a better icing to use? Any tips would be helpful. Thanks in advance!!

Possibly try a stiffer buttercream and / or rolling your fondant a bit thicker.

I had the same issues you are having when I started and found it was a combination of my BC being too soft, and I was rolling my fondant too thin.

As an alternative to BC I LOVE using chocolate ganache under fondant. Smooths nicely, and firms up great to give me sharp edges that I just can't get with BC. Also has a great flavor.

AOk, thanks for the tips. I'll give that a shot. Do you mind giving me your recipe for your ganache!?

My favorite ganache recipe is on my blog, just enter ganache in the search box. 

AOk will do. Thanks again