I have a very creative friend in Southern California. When she told me about what she was doing to create an additional play area for her two children, I asked her to send photos.
Being "green" is all about using the space you already have, more efficiently. My friend certainly did that with an "extra" balcony in her home. As you can tell from this photo, she created a "baby" house out of a little-used balcony off her bedroom. It's every child's dream play house and takes the concept of a tree house to new levels.
I applaud my friend's ingenuity. Oh, and her husband did an amazing carpentry job, for an amateur!