Increase floor area ratio by purchasing green land?

Our floor area ratio is 0.3 because the village is more of a collection of farms. We now have more than enough garden and kitchen garden; the grassland would only become interesting for us if we want to build an age-appropriate house from the old coach house in 20 years. But for that, other outbuildings could also be demolished. It was more of a thought experiment arising from the inheritance case among the grassland owners who are now dividing the estate.

Put differently: if generating building land were that easy, other smart alecks would do it thousands of times, and the whole magic with building land, green land, commercial area, etc. would be obsolete.