Plastic Water Bottles as a Resource

I've been thinking about building a greenhouse- out of scavenged materials, of course- and wasn't satisfied with what I'd come up with. Then I found this, and voila! Instant greenhouse/cold-house for the driveway on the south side of the house.

This whole site is really interesting- his designs are simple, elegant, and functional. I suspect I'd add a bit more support, but overall I love it. Add some passive solar to it and we're in business. What do you think about this design and use of plastic bottles?

http://plentyofbottles.webs.com/apps/photos/

The artist/builder Craig passed away, but his wife is maintaining his website and his Facebook page for now, so please avail yourselves of his wonderful work while you can.

http://www.facebook.com/pages/Zakynthos-Bottle-Recycling/170594736328051