Lot of people saying "don't do it", which are wise words if you have endless other choices. But the reality is that buying a house is very hard for most of us. What you're suggesting isn't unknown and whilst if it goes sour could be extremely pleasant, can equally work out fine and to your benefit. A lot of people start up small housing associations to pull off this sort of thing for exactly the same reasons. Although that involves more than two people, usually.