COTS products have been widely used in large software development and large software systems. They become the key point in large software development and large software systems. If the wrong COTS products are chosen, the project will likely fail. That is why assessment of COTS products is getting more and more attention. There are a few approaches to help people how to do COTS product assessment, but none of them tell people how much assessment is enough. If we do too little COTS product assessment, we might not select the right COTS products; if we do too much, we might not complete the project. People need to know how much is enough when they are doing assessment in large software system development. In this paper, we develop a new approach for making strategic design decisions in determining how much effort (or time) should be spent assessing COTS products with respect to project cost, market window, and a multitude of COTS assessment attributes such as availability, ease of use, maturity, and vendor support. It is a valuable assessment aid when making strategic software design decisions.