Present cost methods used in aerospace conceptual design studies are neither sufficiently accurate nor sensitive enough to design detail to give the visibility needed for choosing between candidate systems. These circumstances lead to the desire to achieve a more fundamental approach to cost estimating, one which reflects the true drivers of design, manufacture, and test costs. The purpose of this paper is to show that: (1) detailed design definition, including such physical characteristics as the total number of parts and pieces and the size and weight of each part, can be achieved with an extension of a typical structural synthesis computer program that is based on analytical descriptions of standard design practice; (2) that a simulated cost buildup can be generated from the parts list by analytically describing standard manufacturing practices, material lists, and the labor time required in each manufacturing step for every part. The paper describes an application of this concept to the estimation of the manufacturing cost of the C-5A vertical stabilizer box structure. Some thoughts are also presented for extending this approach to the estimation of costs of design, tooling, and test through similar emphasis on the fundamental aspects of vehicle design.