If I purchased a hive I would expect a roof to be in the box,
only the delivery box or carton! I expect the roof to go over the hive body, whether above brood or supers, but always there to keep off the rain from the crownboard which is less weather resistant and also to afford a degree of insulation from either extremes of temperature. You do not actually need to buy a pukka roof with the rest of the hive parts, as any old board could be improvised to give shade and shed water, leaving only the insulation concept to be unattended to for the winter months.