This paper proposes performance indices and search criteria for the text script generation in the design of corpus-based TTS systems. Based on the criteria a new search method is presented to solve the text selection problem more systematically and efficiently. Experiment results have shown that with the same hit rate of unit types the new method can reduce up to 40% of text script size in some cases. Furthermore, by control the weighting factor the covering rate of unit types can be increased to improve the robustness of the TTS system. Finally, the scalable and controllable design of the multi-stage search can produce various kinds of text scripts ideally suitable for the requirement of various kinds of corpus-based TTS systems.