5-inch rain gutters are suitable for many homes and buildings with shingle roofs. For tile roofs, however, 6-inch gutters are recommended as they offer more room to accommodate the flowing water from the roof. 5-inch gutters on tile roofing are not recommended as the water is most likely to over-shoot the gutter rather than flow into it.
For flat roofing and any other alternative roofing, a quantified estimator will provide you with a simulated estimate of the size of the gutter to opt for.
