Certain example embodiments of this invention relate to water heaters adapted to be mounted on or proximate the roof of a structure such as a building (e.g., residential home, commercial building, etc.). The liquid to be heated can be water, or other liquid, in different example embodiments. In certain example embodiments, at least one vacuum insulated glass (VIG) unit is provided as part of the water heater structure in order to help preserve heat that has been absorbed and/or generated.