While I'm not knowledgeable on structures, everything about this looks homemade to me. Further proof of that is it seems to be one of a kind. If it were made in a factory, many more would have been built and would probably be known about. Nothing about the way it's constructed would be that hard for someone with a little experience building similar structures.
This corner of the roof that I circled, where the sides don't match up, doesn't make sense to have been made in a factory as I would expect a lot more precision. However, it makes perfect sense for something that was homemade, where the builder may have made a mistake and didn't fix it.
