We had also planned that and then discarded it. Financially, many things would be easier because of it. It sounds harsh, but to be honest, that’s how it is. It sounds great at first when the babysitter is in the same house and you have your parents nearby for care, for example. I don’t know your parents, but it already starts with the jealousy debate. Your girlfriend’s parents could be jealous. You argue more often with people in the immediate vicinity. That could also have effects in the worst case. The parents could always be on your back, etc. Consider all of that. We have talked to many who live like that and most advised us against it. Almost always it was financial circumstances that caused them to build/buy with the parents. How old are your parents? 850 sqm of garden is not exactly small – at least for today’s building land prices. Do they use all of it? How is the property laid out? Elongated? I would have tried to build a single-family house there. 450-500 sqm is enough for the first time. The other part your parents can continue to use as a garden.