The roof cover level will matter in some cases and depends on the building type ( I,II, or III, which is determined by the number of stories of the building) and the year of the building construction.  It only matters on type II & III buildings if they were built before January 1, 2002.  The definitions are shown below from the Citizens manual (found on page 7 of the Rating section of the Citizens CR Multi-Peril manual):

Here are the Wind mit charts for type II & III buildings showing where the roof cover level makes a difference in determining the Wind Mit credit factor (Similar charts for Terrain B):