Hi,
The solution that will work for you is a Battery Powered READ-Write RFID unit that will sit inside the Bonnet and use the inforamtion stored in it to Track the Car and check if it is due for wash or not. A Battery powered RFID will keep sending signals to recievers when someone takes the Reader to that floor or when then enter into the Appartment. The RFID can send Signals upto 300 Feet or more based on the Signal Strength and use this information to do what all you think you want to do.
So, when the person enters the Appartment, he recieves signals from say for eg. 30 vehicles in a row matrix. Each row will say its position, where it is, when it was washed and who did it. Then it will say if is due to wash today. Then he will mark all the cars that are to be washed today and then UPDATE the Car's RFID with information as "DUE to WASH TODAY". Then once the wash is done it is update with three informations. Who washed it, When was it done, Next due date. This information will be written back to the CAR's RFID and then left for the day.
Next day when he comes back, he is again poured with more information as what are the cars to be washed today and it is another day for him.
Then when he brings back the reader, the information that he did for each RFID is posted back to the computer for fure records and references like sending SMS to Car owners, updating their bills etc etc,
IF you think this will work then please kindly reply back and I will be great