Wiring in the Garage

I installed a gable fan in the attic last year. I used Romex (12 gauge). I will be installing a gable fan in the garage this year and I understand that Romex CANNOT be used in the garage unless it is behind drywall. I will be installing an electrical box on top of the drywall, over an existing box (single receptacle), which I will expand to two receptacles. Steel City 2-Gang Square Electrical Box-521711234EW-25R - The Home Depot (http://www.homedepot.com/p/Steel-City-2-Gang-Square-Electrical-Box-521711234EW-25R/202590467) From there, I think the option will either be conduit or armor cable, connected to this electrical box. Please provide your thoughts or recommendation? I am thinking of using armor cable but is there anything more I need to know? I google "armor cable" and AC and MC came up. Any pointers here would be appreciate it. Conduit in the garage just seems like an overkill. Thanks