How should I structure a 16 mark essay to do with the costs and benefits of coastal retreat

For a 16 mark essay you need;-A brief introduction (maximum 2 sentences) which defines the key words (coastal retreat) and introduces the points each parahraph.-3-4 main paragraphs (which follow the structure Point, Example using a case study, Evaluation, Link back to the question). -The paragraphs should either consist of 2 costs and 1/2 benefits or 2 benefits and 1/2 costs, this makes sure that the essay is balanced; focusing on both aspects of the question.-A brief concluson which reiterates the key points and evaluations in one paragraph.
If you were to asnswer the same question but that is worth 8 marks, A conclusion is not necessary however, if it were worth 18+ marks then you would require more key paragraphs which are strongly linked to one another.