Decisions at the early stages of design are critical compared to the later stages of the building design and construction process. This is becoming more evident as the design process and building techniques/materials become more complex. Computers are ubiquitous in later stages while relatively absent in early design stages. One of the consequences of this situation is the need to translate manual design solutions into a format that can be used in computers at the later stages, thus increasing the probability for errors and incompatibilities. This work provides a clear description of the early design process and formulates basic requirements for successfully supporting the process. Existing computer tools are reviewed to determine support for these requirements. An in-depth study, using the technique of protocol analysis of eight designers is carried out to identify possible features for appropriate support. Finally, specifications are defined and then used to create a prototype system for illustration. UPDATE: An effort by the author called Kobldes supporting these findings beyond the prototype, for a building information modeling (BIM) tool, is underway at illom.org.