The choice of caliber for Roan should be based on your choice, the environment, and local regulations. A medium to large caliber rifle such as .30-06 Springfield, .300 Winchester Magnum, or similar cartridges is generally suitable for taking down Roan. Always consult with a professional guide or outfitter to determine the most appropriate caliber for your specific situation and conditions. Pay attention to shot placement and try to make a clean heart or lung shot.