Need to switch objects

im looking to switch my transform (currentobject) to the next item in the list. how would i do that?

public class BuildingSystem : MonoBehaviour {

 public List<buildObjects> objects = new List<buildObjects>();
 public buildObjects currentobject;
 private Vector3 currentPos;
 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;
 private Vector3 currentRot;
 public int switcher = 0;
 private void Start()
 {
     
     ChangeCurrentBuilding(switcher);

     Cursor.visible = false;
     Cursor.lockState = CursorLockMode.Locked;
     
 }

 private void Update()
 {
     if (isBuilding)
     {
         StartPreview();
     }

     if (Input.GetMouseButtonDown(0))
     {
         Build();
     }

     if (Input.GetKeyDown(KeyCode.Q))
     {
         //Switch Object
     }
 }

   

 public void ChangeCurrentBuilding(int cur)
 {
     currentobject = objects[cur];
     if (currentPreview != null)
     {
         Destroy(currentPreview.gameObject);
     }
     GameObject currentprev = Instantiate(currentobject.preview, currentPos, Quaternion.Euler(currentRot)) as GameObject;
     currentPreview = currentprev.transform;
 }

 public void StartPreview()
 {
     if (Physics.Raycast(cam.position, cam.forward, out  hit, 10, layer))
     {
         if (hit.transform != this)
         {
             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;
     currentPreview.position = currentPos;
     if (Input.GetMouseButtonDown(1))
     {
         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 preview;

 public int materials;

 public GameObject prefab;

}