I would not be doing you a service if I told you what you should do in making your model. Remember that the teacher has a learning objective for assigning your project: that you become engaged and look more deeply into the factors involved. Models like this describe assumptions/premises (e.g. that fossil fuels are being depleted and burning changes the climate) and list stakeholders and their roles, and lays out how decisions are made. Good luck!
Here I enjoy the ideas of solar roads the most. Not that's the project that can easily get you the first place. Surely there is no need to build something tremendous but if you manage to explain the idea and attract people's attention, you can win with ease. Here is a great post that can help you understand the concept of solar roads: