A critique of the principle of using markets to assess costs and benefits

A detailed essay plan on the dominant method of economic appraisal, Cost-Benefit Analysis. To explain the rationale for using markets to assess costs and benefits, to identify some problems and suggest a ways of handling those problems. This essay plan will be on two pages with introduction, one key paragraph and conclusion written in full.
In introduction part I need to lay out the structure of the argument of the essay. Key paragraph would be a statement of what is the key argument you would develop. Conclusions would summarize the arguments that you would have developed had you written the essay in full.