I think CPhill's idea is floored, he hasn't considered that some of the area is used by both of you.
I think it is because his his triplet siblings are perched on his head! What a heavy weight to bare! Poor CPhill. Maybe 6 eyes are better than two when you are seaching for a Roman 0.
LOOK IN THE BOULDER SIR CPHILL AND SIB'S - 'TIS IN SISYPHUS'S BOULDER!!
(It is an in joke - don't worry - we are all crazy here!)
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Let me see.
Here's the way to do it...
Work out the
1) common area footage
2)your area footage
3)roommate's area footage
To figure your share, it's just...
[(common area/2+your area)/ (total square footage)] x rent
And your roommate's share is just
[(common area/2+roommate's area)/ (total square footage)] x rent
Do you know how to work out each area?