If you are planning to travel from and to NDLS for a day or 2 , and you want to use your car , the Airport Metro car parking on the AJmeri Gate side is a perfect option. You get the parking easily, (unlike the railway parking which is always full/near full), it is more orderly with defined parking lots, it is covered parking means your car is safe from sun and rain.
The metro car park charges rs 200 per day, which is same as the railway car parking.