Its made of "wood" aka sheets of wood glued together, and lightweight trusses. These are also used in most new construction homes. They are highly sturdy and supportive in everyday use. If you have a fire, they will fail very quick. The trusses don't hold well to heat (summer heat is ok.. Fire heat no no), and the glue (chemicals) holding the wood sheets together are an accelerant. The wood will also burn much quicker than a beam of the same size due to variance in density. Even if your horses escape a fire, the burning chemicals are very high risk to the respiratory tract (ie: possible lifelong issues/death). Also I don't know how much snow you get, but keep an eye on the roof loads (found on FAQ page). If you could afford something made a bit more sturdy with real wood beam and heavy duty trusses, I would definitely take that route.