An icosahedron is 20 sided figure. You will find complete directions to give to students as well as a rubric to help you grade the project.
I personally give the students 4 weeks to complete the project. Each week, the students needs to bring me 5 circles to check. I make comments on a sticky note to give to them about their circles. At the end of 4 weeks, they have comments from me and will be ready to assemble.