QUOTE (Mardrax @ Feb 2 2011, 01:09 PM)

Emphasis mine.
How are you calculating that, Infinity?
My interpretation is:
RAW doesn't mention wether to use base or modified lifestyle costs for this, but base seems the logical thing, resulting in:
The final cost should be 5000+500-1000=4500, divided any way you choose. Wether this results in the ogre taking full advantage of his stomach, the costs being split into 2750 each, minus 1000 for the ogre, or them sharing in the goodness and paying 2250 each really is irrelevant, and should be discussed among the players in question.
If the roommate has an Ogre Stomach or similar benefit as well, I really don't know how to call it. I'd probably roll with making him add 400 to the total cost. This doesn't make sense, considering how much of the extra 500 should be taken up by food, but neither does the full 20% cut an ogre gets.

What you've calculated for the single-ogre-stomach scenario is exactly how it should be handled for the double-ogre-stomach scenario, since they'll have the same nutritional requirements and benefits as each other. Giving a full discount when only one of them has the augmentation has to be wrong. It's when there's only one ogre stomach that the issue gets contentious.
If you rule, as in your first post, that the two room mates will eat the same despite that only one has the ogre stomach advantage then cost it as with two ogre stomachs (discount of 1,000) and see how long it takes for the room-mate to die from malnutrition (or eat the primary character).
If you rule that one character will take advantage of having an ogre stomach whilst the other one can't/won't, then it depends on how you see it. If you consider that the savings (technically 90%) from two people co-habiting should be considered still applicable to their dietary arrangements then you only grant half the discount for the ogre stomach but of the entire amount, making it 10% of 5,500 – how they split the 4,950 rent is then up to the characters. Alternatively, one might argue that if the two are eating so differently then there should be no savings for efficiency where food is concerned – this means then that the 20% discount should actually apply to the room-mate charge and that alone (since the other guy needs to spend as much on nourishment as he would if living alone) and 20% of 10% of 5,000 is 100, so total lifestyle cost comes to 5,500 - 100 = 5,400.
Not that this level of analysis is especially fun at the gaming table, but it is interesting to work through the logic in one's lunch hour!