It would help to know the roofing material and slope.

If it is almost flat, black and feels like a sheet of rubber, it is probably EPDM (synthetic rubber). You can probably buy a small roll of self-adhering EPDM at a lumberyard and patch it yourself if you can find the hole (which could be small or numerous). You should buy a spray-on cleaner and apply the patch in moderate to warm temperatures using a small roller to press it down along the edges.

If it is built-up asphalt with gravel on top you need to hire a roofer.

Patching low-slope roofing with an incompatible material will most certainly fail.

Hire a reputable roofer that is familiar with your roofing type and in writing will back up the repair.

Make sure they are legal, licensed, insured and get referalls and check them out. It's a good idea to get more than one estimate and not go necessarily with the lowest bid, but rather the one who's reputation is intact. If your state has a licensing board, you can check on them by posting their states license number for any negatives against them. Sounds like a lot of effort for a repair, but you dont want a hack up there who wont do it right the first time around and chances are, you could have bigger problems than just the one leak that they can inspect for you.

as i am not sure of the material but i think it is not the synthetic rubber one of course.
I will hire a roofer, i do not know any in my area but i consulted my neighbor and he told me about one.
i have called him. he will come this weekend. thanks guys