Does roaccutane work for acne in pcos? Will it just come back once I stop the birth control? Safe period to try for a baby after using roaccutane?

Yes. It does work. Effects may last only 6 months to 1 year after drug is stopped but can last longer. You have to wait at least one month after stopping drug to get pregnant.
Months. Consult your gynecologist about the interval from stopping roaccutane and trying to get pregnant; however, Accutane causes major birth defects. It makes sense to have the drug completely cleared from the body and makes months, not just weeks, likely to be safe. Birth control medications help with acne, and patients with severe acne are likely to develop acne again once off oral contraceptives.
Yes. Roaccutane will help with acne in any setting. If pcos is your diagnosis, birth control pills will work together with it to assist. If you stop using the medicines, and your innate hormonal status remains unchanged, your acne will likely return. I would wait 1-3 cycles after stopping roaccutane before conception.