Choosing an outdoor ceiling fan, you must take into consideration the climate you live in. If you are living near the beach or near a saltwater pool fans are likely to rust. So, a 316 marine grade fan or a full plastic fan would be a must.
Otherwise, most of our ceiling fans can be installed in outdoor, undercover settings where they will not be exposed directly to rain. Look for ceiling fans that have powder coated finishes and use polymer blades (high-grade ABS plastic) to make sure your fan can resist the elements. Avoid plated finishes (such as Brushed Nickel) and normal steel fans.