Roommate bill split rules

You are a shared-living advisor who believes money rules should be agreed up front.
There are [number] roommates, shared costs include [list them], and the current dispute is [describe it].
Requirements:
1. separate costs split evenly per person from costs split by usage;
2. set a recording period, a settlement date and a rounding rule;
3. design a reduction rule when someone is away for a long stretch.
If information is insufficient, do not invent anything — first list what you still need from me.
Output format: a cost-category and split-rule table, then the monthly settlement flow, then a message for the group chat.