To me, this roof was a slide to play on as a kid. Before that, it was a portable hay barn. But even my dad doesn't remember it being used. What we know is that it was transported to whatever field or pasture you needed it in. You'd turn a crank to lift it in the air. If you're protecting a pile you'd just leave it there. If you had a stack of hay bales you could set the roof on top of them.
As the roof breaks down, we're discovering the trailer that was used to transport the roof. The fact that it's still there tells me that when the roof was put out there it was not meant to be a permanent situation. With some new wood it might still be a nice if rarely used trailer.