Design a small network connected to the Internet. Five or six computers should be enough.
Think about servers you might need, such as mail, web, dns, etc.
What about a print server?
How will you connect to the Internet?
Will you use wireless?
What about a firewall?
You need to prepare a diagram that shows how everything is connected and write up a brief description of the diagram explaining what components you chose, why you chose it and what it is for.