Google seems to be failing me on how feasible this is. In the US, it's (relatively) easy to buy land to build your house on, or to buy an existing farmhouse because we have farms and farmland everywhere. But is it the same for Germany? Money is really no object, he's rather independently wealthy.
Alternatively, if houses that big are available in that area (I say Dortmund because the family is familiar with it, but it could be anywhere as long as it's within easy driving distance of Meschede), could someone point me there? I couldn't find anything bigger than four bedrooms.
Edit: Thank you all for your help! I love this community. Everyone is always so wonderful. ♥