I have 2 at the moment and a 3rd going in in the next month or so before Autumn. I built the 1st two out of some Ikea headboards!! They are 3 years old and still going strong!
The 3rd is an old 210Ltr plastic water butt with a hole in it thanks to the ice cracking it.
So annoyed I left water in as they are expensive here in Sweden but still I can recycle it.