Automatic parking System

I am totally new to electronics and circuits so I know very little. My idea is of an automatic parking system.
There will be two stories. Maximum 4 cars can be parked in the ground floor. Now there will be an LDR and a counter to count the no. of cars getting in. As soon as the counter counts the fifth car, a circuit will get on and a lift will start working carrying the fifth car to the first floor. A timer will hol the motor of the pulley of the lift to keep it steady there for some seconds and hen will take the lift down.
Is this project possible?? If possible please help me with the circuit as quickly as possible.

I see trouble with a counter to hold the lift in place...
If you're using sensors and counters on incoming cars, it's just as easy to 'sense' when the car leaves the lift.
Also, why not sense how many cars are parked on the ground floor, so if one of them leaves, you can let another park there.

We have changed the idea a bit. The LDR will sense the fourth car when it gets parked inside the lot. Then the gateway A will get closed as in a level crossing where a bar comes down to block the way. After that all the next cars must go through gateway B. Now at B, there is a lift which has another LDR inside which when senses the car inside, goes up automatically.
I think the problem about the counter is not here. There will possibly be two circuits:- one to control the bar for gateway A, and the other will control the lift. Both will work with the help of sensation by the LDR.
I have attached the diagram here:-

Please will you be able to make the diagram for the circuits??