Related to "case study" part, you need to find examples of other bench designs. Through "case study", you can get some idea howto design a bench for your group project

#1. For example, you can find bench examples with different design / shape and you can apply these for your bench.you can also find bench examples with different materials and you can choose material for your bench.And, you can write about the reasons for your final selection and the reasons why you don't select other options.