Gst for renting of vehicle

I am registered under gst as regular tax payer.i am providing vehicle (car) with fuel and driver to department of railway on contract basis.they tell me to charge gst @ 5 %and I am paying tax.is iam liable to take itc? of goods purchased for my office? iam also providing other contract services to dept. of railway.like some small construction work so can I avail the itc on cement,sariya purchased for that?