Enemy/zombie spawner

im making a zombie game like the last stand, but i dont know how to make the zombies respawn at a certain place every few seconds. please can anyone help me?

You can create a spawn script like this:

using UnityEngine;
using System.Collections;

public class Spawn : MonoBehaviour
{
  // Spawn location
  public Vector3 spawnLocation = Vector3.zero;
  // Spawn radius (Gives a bit more randomness factor to the spawn location)
  public float spawnRadius = 1.0f;
  // Spawn timer (seconds)
  public float spawnTimer = 5.0f;
  private float spawnTimeRemaining = 5.0f;

  // The zombie to spawn
  public GameObject zombiePrefab = null;

  void Awake()
  {
    spawnTimeRemaining = spawnTimer;
  }

  void FixedUpdate()
  {
    spawnTimeRemaining -= Time.deltaTime;

    if (spawnTimeRemaining < 0.0f)
    {
      Vector2 circlePosition = Random.insideUnitCircle * spawnRadius;
      GameObject.Instantiate(zombiePrefab, spawnLocation + new Vector3(circlePosition.x, 0.0f, circlePosition.y), Quaternion.identity);

      spawnTimeRemaining = spawnTimer;
    }
  }
}

Thats one way of doing it. If there are any errors in the code, then I'm sorry, but its of the top of my head :)

Oh, and remember to set the zombiePrefab variable, else you will get null reference exceptions.