Maybe i've watched one too many episodes of Grand Designs, but there is something quite attractive about creating something yourself that is fit for purpose, meets all your needs, and incorporates 'green' design features. The other advantage is that it would seem as though you get a lot more house for your money.
If there were 3 or 4 couples wanting to be part of this, i'm guessing that we would be needing about 8 bedrooms as minimum. To buy something of this size that has a bit of land around it is looking pretty expensive (although there are a few surprises out there). By creating something yourself you can make spaces that work. It may be that it is designed with 4 separate family spaces that all join to a central living space and large kitchen. I would also love to see things like rainwater harvesting, ground source heat pumps, grey water recycling, under floor heating, and lots of solar or other renewable energy generation.
From a quick bit of internet scouring, it would seem that you would probably need to spend at least 600K to get a decent size property that would still need a lot of work, but i wonder what 200K on land plus 400K on the build would actually get you?
Anyway, these are just my thoughts - i'd love to know yours