As process technology scales, the design effort and nonrecurring engineering (NRE) costs associated with the development of integrated circuits is becoming extremely high. Structured ASICs offer one solution to these problems. However, to realize their full potential, their performance and cost advantages, architectures, and CAD must be fully understood. We believe that this can lead to wider adoption of structured ASICs. In this paper, we take a step in this direction and investigate the area, delay, power, and cost tradeoffs in metal-programmable structured ASICs (MPSAs). In particular, we quantify the impact of the number of user-defined (custom) metal mask layers on these metrics. Results indicate that for lowest cost, the number of custom layers should be minimized, especially for small die sizes (e.g., less than 100 ${\hbox {mm}}^{2}$). Delay and power, however, can be improved by a few additional custom layers. With two custom metal layers, MPSAs can be 2$\times$–10$\times$ cheaper than cell-based ICs (CBICs).