My fiance and I are in the process of buying our first home together and have offered to let a friend and her son move in with us and "pay rent" (part of the mortgage + utilities). Now, we're not concerned (yet) about sharing spaces, etc., but my fiance does have a bit of a hang up on the payment situation.
Due to city housing ordinances, my friend's son is required to have his own bedroom, so she will essentially be taking two bedrooms while my fiance and I have one. He thinks our friend should be paying more than just half because she's taking more space — but the whole point of this exercise was to help her pay less so she can pay off credit cards and medical bills. My suggestion was that all of the adults (myself, fiance, and friend) all pay in equal "budget" (such as $500) to cover bills and mortgage and anything left over goes towards house renovations or something else.
Homies, how have you worked out splitting the costs between roommates in such a situation before?