This is an old idea, finally I have the time to show it to the world.
The are bottle shapes that perfectly fit together, you will see how easy it is to create a wheel from two plastic bootles, the video speaks for itself.
Check this project to see how I attached the wheels to a continuos rotation servo motor.
Nice. And light weight too,
Nice. And light weight too, if one should have focus on that 
I like your idea too,great
I like your idea too,great ignitiative. I would also think of using plastic bottles on water as floaters and with a bit of modifications they might rotate too 
Sorry for double post.
" if one should have focus
" if one should have focus on that :)" what do you mean? focus on what?? 
excelent
it’s an helpful trick XD