These 'non-functional constructions' are a side shoot from building houses and farming, in that they are often made from materials left over from a building project or farming process, and might use similar methods of assembly. Most are made to be outside and withstand the local climate. Some pieces can only last a year or two outside before deteriorating at which point they come inside, having been sufficiently weathered. Sometimes things don't survive and so get dismantled and recreated into a different form.