How can I make a "Fastest Lap" scoring system for a racing game?

I am making a racing game and need a scoring system. I want it to count the time that it took to do a lap and that you get more points if you do the lap faster (the faster you finish the lap the more points you get). So how do I script or make it?

all right! make a cube, turn it into a trigger (check "isTrigger") and tag it "FinalLap" you'll add this script to your car or whatever you'r racing. and turn off the mesh renderer.

var points = 0;

function OnTriggerEnter(hit : Collider)
 if(hit.gameObject.tag == "FinalLap")

function Update()
 print("I finished in: " +points); 
function Finish()
 if(Time.time <= 90) //if you make it before 90 seconds
  points += 5; //add points
 if(Time.time <= 50) //if you made it before 50 seconds
  points += 10; //add points

that should add points based on the time it took to hit the trigger (box) and prints in the Debug.Log that you finished in a predefined time.

hope this helps!!!

The way I implement this is to have a series of waypoint positions around the track which are collected together as an array of Vector3s. (See here for more detail on that)

I then track each waypoint that the user passes using a simple "Dot" vector function. Because I know how many waypoints there are, I can track when the user has passed the last one, and begin checking for the first waypoint again. Whenever the first waypoint is passed, I update the lap counter, and record the lapTime.

This method also gives you easy access to how far around the track a user is (eg, if they've passed 45 of 150 waypoints, they have completed ((45/150)*100)% of the lap!

int lapNum = 1;
int waypointNum = 0;
Vector3[] waypoints;  // this should be filled with vector3 world positions
                         as show in answer linked above in this question

void Update()
    // we get the current target waypoint and the next waypoint 
    // (in order to calculate the waypoint's direction)
    waypoint = waypoints[waypointNum];
    nextwaypoint = waypoints[ (waypointNum+1) % waypoints.Length ];

    // route direction at target waypoint:
    waypointDirection = nextwaypoint - waypoint;

    // delta from car to target waypoint
    Vector3 waypointDelta = wayPoint-transform.position;

    // check whether car has passed target waypoint, using Dot Product
    if (Vector3.Dot( wayPointDirection, waypointDelta ) < 0)
        // if so, step to the next waypoint number.

        // check whether we passed the last one
        if (waypointNum == waypoints.Length)
            // we completed a lap. record time and reset waypoint tracking to zero.
            lapTime = (Time.time - lapStartTime);
            if (lapTime < fastestLapTime) {
              // new fastest lap!
            waypointNum = 0;
            lapStartTime = Time.time;