i can fly trough objects

i need help i can fly trough objects with a fly script

here is the script

using UnityEngine;
using System.Collections;

public class flycs: MonoBehaviour {

    public enum RotationAxes { MouseXAndY = 0, MouseX = 1, MouseY = 2 }
    public RotationAxes axes = RotationAxes.MouseXAndY;
    public float sensitivityX = 15F;
    public float sensitivityY = 15F;

    public float minimumX = -360F;
    public float maximumX = 360F;

    public float minimumY = -60F;
    public float maximumY = 60F;

    public float minimumZ = -60F;
    public float maximumZ = 60F;
    public int speed = 5;
    public Transform EmptyGameObject;

    float rotationY = 0F;
    float rotationZ = 0;

    void Update ()
    {
        float motorForce = 1+(speed * Input.GetAxis ("Vertical"));  

        Vector3 moveDirection = transform.TransformDirection(Vector3.forward);
        transform.position += (moveDirection * motorForce) * Time.deltaTime;    

        if (axes == RotationAxes.MouseXAndY)
        {
            float rotationX = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityX;

            rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
            rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);

            transform.localEulerAngles = new Vector3(-rotationY, rotationX, rotationZ);
        }
        else if (axes == RotationAxes.MouseX)
        {
            transform.Rotate(0, Input.GetAxis("Mouse X") * sensitivityX, 0);
        }
        else
        {
            rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
            rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);

            transform.localEulerAngles = new Vector3(-rotationY, transform.localEulerAngles.y, 0);
        }
    }
}

the basic's are from the mouse look script that comes with unity with a move script attack to it

please help me

You actualy need to use physics engine to get any cld working:

http://unity3d.com/support/documentation/Components/comp-DynamicsGroup.html