basic design completed
A structure's design has enough specifications to distinguish it from other designs or iterations for the same site.
The basic design for a structure is formed when sufficient specifications are given to provide enough data to identify it as a structure and to avoid confusion with any other iterations of plans for the same site or similar structures. This event's occurrence is a prerequisite for the structure having any status at all, even as a visionary structure.
The specifications must identify this design separately from alternative plans for the site. An undifferentiated idea to build something there does not meet that requirement.
Conception can precede the identifiable design and be recorded afterward. Basic design completion does not require the design to be an active proposal; it is also required for a visionary structure.