Just saw this post and loved the idea. Not only is it cute but very green! Saving our environment is important and I just love repurposing things. This post is from http://chiccottagejunk.blogspot.com/#.
There are so many old lamps and old bowls that you can find at thrift shops and flea markets that this would be very easy to do. I think the old metal lamps would be my choice. I could see how the patina could change over time with exposure to the elements. Don't use anything with dangles though, this will scare the birds away!