This article addresses the pressing scientific and practical challenge of ensuring the accuracy of cost estimates in the early stages of investment and construction projects, when detailed design solutions are lacking. A critical analysis of the current cost estimate system is provided, identifying its systemic shortcomings, including regulatory inertia, regional variability in construction conditions, the impact of market volatility, and the subjective human factor. As a methodological solution, a proprietary methodology for generating aggregate cost estimates is proposed, based on a synthesis of the principles of hierarchical decomposition of an object and progressive packaging of works. The methodology was tested using the example of calculating the cost of constructing a multi-layer external wall using current state elemental cost estimate standards and a federal collection of cost estimates. The results of the test demonstrate the practical validity of the approach: the discrepancy with the results of a detailed traditional calculation was 13.25%, which is within the acceptable accuracy standard for the pre-design stage. In conclusion, the potential for implementing the methodology is substantiated and promising areas for further research are identified, the key one being the integration of the developed approach with building information modeling (BIM) technology to automate costing processes.