Admittedly, it will take quite some time to collect all the bottles needed for this project by yourself, by I think if you get your friends, neighbours and family to start saving up their bottles as well, it shouldn’t take too long. The important thing is to get started saving your bottles right away. As I see it, the biggest roadblock with the project is the space required to store all the plastic bottles whilst you are saving them up.
If you are interested to know more, or you want to give it a go, you can download a PDF document showing how the greenhouse was built. The PDF also includes plans and a shopping list of the other materials you need to build your own soda bottle greenhouse.