Final answer:
The continuous supporting surface extending horizontally throughout a building, which constitutes one level in the structure, is referred to as a Floor (option 1). This is an essential concept in building construction and is depicted in floor plans used by architects.
Step-by-step explanation:
The subject of the question is from an architectural point of view, specifically looking at the different parts of a building's structure. The best answer is 'Floor,' which is a continuous supporting surface extending horizontally throughout a building, constituting one level in the structure. This key element is part of the basic building construction process, which starts from laying the foundation and building up.
The provided options such as 'Ceiling,' 'Wall,' and 'Roof' have their unique purposes - the ceiling is the overhead interior surface, the wall is a vertical barrier, and the roof is the top covering of a building. In architectural terms, a floor plan helps architects to detail the layout of each level of a structure, showing the arrangement of rooms and other spaces.