Another helpful article is found on the Austin Tenants' Council website-
After determining how many roommates there will be, consider how much rent each person can afford. Generally, 30 percent of a person’s income is considered an affordable housing cost. Other expenses such as utility bills, phone bills, and cable TV bills should be included in calculating what can be afforded. There are many up-front costs when renting such as security deposits, pet deposits, utility deposits, and installation charges. Except in an “all bills paid” unit, these items are extra.
Ensuring that all roommates can afford to pay the rent and other expenses is the best way to avoid problems. Careful preparation and assessment of financial resources will prevent any roommates from getting in over his head and jeopardizing the other roommates’ credit and rental histories.