When referring to the highest level of a building, "upper story" is a commonly used term. However, there are a few synonyms which can be used interchangeably with this phrase. "Top floor" is a straightforward and commonly used substitute, while "attic" or "loft" refer to specific types of upper stories. "Garret" is an older term used to describe a small attic or room at the top of a house, typically used for storage or living quarters. Alternatively, "penthouse" typically refers to a luxurious apartment or living space located on the highest floor of a high-rise building. These synonyms add variety to language and provide a more descriptive way of referring to an upper story.