Both architect and interior designer are two professions that have different focus and responsibility, although both have the same objective to make the building nicer, they also have an ability to design a house or building with an aesthetic and safety value, and able to help you build a nice and cozy place as you wish.
An architect was assigned to plan and design all types of buildings, not only a house, but also schools, holy places, stations, hotels, apartments, etc. An architect work closely with numbers, lines, and corners, that combined and arranged in a blueprint/mockup. Architect able to combine the functions of room/building, safety, and needs of the blueprint/mockup.
Meanwhile, an interior designer, professionally trained in develop design plan for all building’s interior, including hotel or office building. An interior designer will discuss with clients and make blueprint. This design will emphasize aesthetic appearance for interior space. Interior design will be more focus on aesthetic appearance when creating blueprint/mock up or building, the design need to contains comfortability, efficiency, effectivity, and safety elements in all rooms they designed. Start from choosing furniture, layout, lighting, color, ceiling, and floor pattern as well.
Shortly, architect will design an interior and exterior appearance of a building from the place that will be built. On the other hand, interior designer tends to focus more on creating a desired look and function for spaces inside a building.
So, to answer the question above, it depends on your needs. If you are planning to make a design plan (blueprint) a building from the beginning, it’s recommended to use both architect and interior designer. But if you want to make a re-construction, then you need to consult with the architect, but if you only need to re-decorate your room with an aesthetic touch and desired look on a building that you already have, then you can consult with an interior designer.