Unet Instantiate

I have this simple building script, where if i press q i can build objects, like a foundation. But this doesnt sync over UNET? How would i make this script sync over unet?

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.Networking;
 
 public class BuildingSystem : MonoBehaviour
 {
     public List<buildObjects> objects = new List<buildObjects>();
     public buildObjects currentobject;
     private Vector3 currentpos;
     private Vector3 currentrot;
     public Transform currentpreview;
     public Transform cam;
     public RaycastHit hit;
     public LayerMask layer;
 
     public float offset = 1.0f;
     public float gridSize = 1.0f;
 
     public bool IsBuilding;
 
     void Start()
     {
         ChangeCurrentBuilding(0);
 
         Cursor.visible = false;
         Cursor.lockState = CursorLockMode.Locked;
     }
 
     void Update()
     {
         if(Input.GetKeyDown("q"))
         {
             IsBuilding = true;
         }
         else if(Input.GetKeyDown("e"))
         {
             IsBuilding = false;
         }
 
         if (IsBuilding == false)
         {
             currentpreview.gameObject.SetActive(false);
         }else
         {
             currentpreview.gameObject.SetActive(true);
         }
 
         if (IsBuilding == true)
         {
             startPreview();
         }
         if (Input.GetButtonDown("Fire1"))
         {
             Build();
         }
         if (Input.GetKeyDown("0") || Input.GetKeyDown("1") || Input.GetKeyDown("2"))
         {
             switchCurrentBuilding();
         }
     }
 
     public void switchCurrentBuilding()
     {
         for (int i  = 0; i < 3; i++)
         {
             if(Input.GetKeyDown("" + i))
             {
                 ChangeCurrentBuilding(i);
             }
         }
     }
 
     public void ChangeCurrentBuilding(int cur)
     {
         currentobject = objects[cur];
         if(currentpreview != null)
         {
             Destroy(currentpreview.gameObject);
         }
         GameObject curprev = Instantiate(currentobject.preview, currentpos, Quaternion.Euler(currentrot)) as GameObject;
         currentpreview = curprev.transform;
     }
 
     public void startPreview()
     {
         if (Physics.Raycast(cam.position, cam.forward, out hit, 10, layer))
         {
             if(hit.transform != this.transform)
             {
                 showPreview(hit);
             }
         }
     }
 
     public void showPreview(RaycastHit hit2)
     {
         currentpos = hit2.point;
         currentpos -= Vector3.one * offset;
         currentpos /= gridSize;
         currentpos = new Vector3(Mathf.Round(currentpos.x), Mathf.Round(currentpos.y), Mathf.Round(currentpos.z));
         currentpos *= gridSize;
         currentpos += Vector3.one * offset;
         currentpreview.position = currentpos;
         if (Input.GetButtonDown("Fire2"))
         {
             currentrot += new Vector3(0,90,0);
         }
         currentpreview.localEulerAngles = currentrot;
     }
 
     public void Build()
     {
         PreviewObject PO = currentpreview.GetComponent<PreviewObject>();
         if (PO.IsBuildable)
         {
             Instantiate(currentobject.prefab, currentpos, Quaternion.Euler(currentrot));
         }
     }
 }
 
 [System.Serializable]
 public class buildObjects
 {
     public string name;
     public GameObject prefab;
     public GameObject preview;
     public int Gold;
 }