My dear daughter just hit me with Sept 20,2014 for her wedding. More than likely an outdoor reception.

We are in Myrtle Beach South Carolina USA

Has to be at least 3-4 tiers (just because both of my nieces where last year). 

QUESTION: how will fondant hold up? I never use it but butter cream will not make it outside in the heat. 

Fondant would do well, but I would suggest using ganache under it instead of Buttercream so that the heat won't affect it as much.

Charlotte's Whipped Cream Buttercream  WILL stand up to heat and humidity.  Srsly.

IndyDebi's Buttercream will also hold up.

Awesome Leah, I've never used Charlottes or Debbie's. I will have to try them.

ASharon's Sugar Shack recipe will also hold up to the heat. I use it on all my cakes. I think it was two years ago I had a 5 tier cake in June for an outside. Temp was about 90 degrees (record breaking heat that day). Everything was perfect.

http://cakecentral.com/g/i/2355226/a/2356226/tier-were-14-12-10-8-and-6-lemon-cake-with-lemon-and-strawberry-filling-for-some-tiers-white-cake-with-strawberry-filling-and-fresh-strawberry-chunks-in-other-tiers-pictures-by-darlene-hall-photography/

Thank you good idea 

 I live 2 hours away from Myrtle Beach. It gets pretty hot in September. I hope your daughter decides to have an indoor reception. It is a lot better not having to worry about the butter cream  melting. It sounds like there are a few cakes with butter cream that will work with high heat but I would still worry about it melting.  I remember seeing a video of a woman who put a butter cream cake outside in 90+ degree weather and it melted.

Congratulations on your daughter getting married!!