Hi Mariwan Abdullah,

Your question does not give clear details about the problem. However according to contents available from your question, we are providing you the solution to your problem.
As you stated that roof slab of the house is of cement concrete, water accumulate in some area and has bad finishing. This shows that you have not treated the top roof of the slab. You should treat the roof slab according to the method given below.
1. Apply bitumen on top of the slab after cleaning.
2. Lay polythene sheet on bitumen surface of the slab.
3. Lay earth 2-3 inch, thick and make proper slope in earth towards rainwater pipe to drain out of rainy water.
4. Lay brick tiles with mud mortar on the compacted earth.
5. Finish brick tiles top with cement pointing.
6. Construct cement concrete gola at the junction of the slab and parapet wall.
Thanks.