Depends on the country - some fields are better used for construction, farming or just being left as a natural habitat. And the roofs can't be used for any of t

Depends on the country - some fields are better used for construction, farming or just being left as a natural habitat. And the roofs can't be used for any of those three things. So... But it depends on the country. Some countries have a whole lot of "low use" fields, like natural or industrial deserts. Others don't.