If I were you, I would request 15k for basic salary plus 6k for housing, 2k for transportation, annual return ticket and health insurance. (Health insurance is important, normally people visit private hospitals and it will cost around 300-400 for consultant without insurance.)

How about checking costs of everything you need in Qatar through the internet or this site and just sum up. You might get your answer.

Anyhow, if you once contract with wrong company to work for, it is very difficult to change. Because of sponsor system in this country. Be careful!