What must the boundary sketch be when creating a floor in Revit?

When creating a floor in Revit, the boundary sketch must be closed. This means that all the lines of the sketch must connect back to the starting point without any gaps. A closed boundary ensures that Revit can accurately interpret the area defined for the floor, allowing it to generate the correct geometry and volume for the floor element. A closed boundary not only defines the physical limits of the floor but also allows Revit to compute properties such as area and material patterns accurately.

An open boundary would result in an incomplete or undefined area, preventing Revit from knowing how to interpret the floor shape. A flexible boundary might imply that the shape could change, but this concept does not directly apply to the requirement for a floor boundary. Lastly, while defined boundaries suggest some form of clarity in the sketch, it does not guarantee that the boundary is closed and would not fulfill the requirements for creating a proper floor in Revit.