Abstract
This paper considers problems of elicitation, documentation and validation of user requirements, and implicates the need for method that enables the stakeholders to resolve problems of incomplete, incorrect and contradictory requirements in the earliest possible phase of project. Review of research literature shows that the existing methods are primarily intended for requirement engineering and software engineering professionals and that there is a lack of method that will ensure the active role of business users. This paper defines new method of elicitation, documentation and validation of users requirements based on complementary application of Event Process Chain method and UML language. Its experimental part verifies and evaluates the suggested method on specific project of customized software development. This method is suitable for early software size estimation. New metric for estimation of software size and complexity is developed.