Some folks are going for DST arrangements.

You can find a way to live free or cheap through a house-hack or AirBnB arrangement in most markets. 

I would then confirm exactly when they plan to be out and arrange to pick up the keys and do a walk-thru on that date.  

I was hoping this was a more common arrangement and there was a known simple way to calculate a persons investments value into a shared property 

., BLK 1.71% platforms such as Fundrise and Roofstock that buy and arrange for the management of rentals on behalf of individuals and builder LGI Homes Inc., LGIH 2.47% which now reports wholesale home sales to bulk buyers in its quarterly results.

Before me there was another guy with the same arrangement.

How do we arrange that so I’m not paying for the roof and then I’m put money in case something else goes wrong?

I don't know your market but how much could you get for your friend's bedroom and bathroom assuming he finds other living arrangements?

How should the contract be arranged? 

Older folks are used to that sort of arrangement.