The greenhouse in the country: do with their hands out of PVC pipe. Detailed instructions with diagrams for the greenhouse of plastic pipes. Two variants of the greenhouse: one entirely of PVC pipe, the other of the pipes on a wooden frame.
Wall mounted ball run. This would be great for kids who are too young for the marble runs. Could be used as a music installation if there are movable obstructions in the pipe that make sound when a ball touches them
Your house is defined by its interior as well as its exterior. Most people focus on decorating the inside of their homes and forget about their backyard. In fact, paying attention to your backyard is as important as decorating the inside of your home.