Trouble with Minecraft like building

How would I go about creating a way to build things in a game in a way that is similar to Minecraft but allows for non-cube block dimensions.

I currently have a partially working method but in some instances the object will be not align to an already existing object.

Here is an example.

Here is my current code.

 Vector3 TempInstScale = TempInst.transform.localScale;
 
         if(Input.GetKeyDown(KeyCode.Keypad8)) {
 
             TempInstScale.x += 0.2f;
 
         }
 
         if(Input.GetKeyDown(KeyCode.Keypad2) && TempInstScale.x > 0.2f) {
             
             TempInstScale.x -= 0.2f;
                 
         }
 
         if(Input.GetKeyDown(KeyCode.Keypad9)) {
             
             TempInstScale.y += 0.2f;
             
         }
         
         if(Input.GetKeyDown(KeyCode.Keypad3) && TempInstScale.y > 0.2f) {
             
             TempInstScale.y -= 0.2f;
             
         }
 
         if(Input.GetKeyDown(KeyCode.Keypad7)) {
             
             TempInstScale.z += 0.2f;
             
         }
         
         if(Input.GetKeyDown(KeyCode.Keypad1) && TempInstScale.z > 0.2f) {
             
             TempInstScale.z -= 0.2f;
             
         }
 
         if(Input.GetKeyDown(KeyCode.Keypad5)) {
             
             TempInstScale = new Vector3(1, 1, 1);
             
         }
 
         TempInst.transform.localScale = TempInstScale;
 
         TempPlaceObj.transform.localScale = TempInstScale;
 
         float GridSize = 0.2f;
 
         if(HotBar[HotBarSlot].Item_Type == Items.ItemType.Block) {
 
             Ray rayplc = cam.ScreenPointToRay(Input.mousePosition);
             RaycastHit hitplc;
 
             if(Physics.Raycast(rayplc, out hitplc, 50  + GameObject.Find("PlayerCam").GetComponent<CameraControl>().DistanceToTarget)) {
 
                 TempPlaceObj.SetActive(true);
 
                 Vector3 pivotpoint = (hitplc.point + hitplc.normal / 2) - hitplc.transform.position;
 
                 if(hitplc.collider.tag == "Ground") {
 
                     if(TempInstScale.y == 1) {
 
                         pivotpoint.y = 0.5f;
 
                     }
                     else
                     {
 
                         pivotpoint.y = TempInstScale.y / 2;
 
                     }
                 }
 
                 float tileX = pivotpoint.x / GridSize;
                 tileX = Mathf.Round(tileX);
 
                 float tileY = pivotpoint.y / GridSize;
 
                 if(hitplc.collider.tag != "Ground") {
 
                     tileY = Mathf.Round(tileY);
 
                 }
 
                 float tileZ = pivotpoint.z / GridSize;
                 tileZ = Mathf.Round(tileZ);
 
                 float WorldX = hitplc.transform.position.x + tileX * GridSize;
                 float WorldY = hitplc.transform.position.y + tileY * GridSize;
                 float WorldZ = hitplc.transform.position.z + tileZ * GridSize;
 
                 Vector3 WorldPos = new Vector3(WorldX, WorldY, WorldZ);
 
                 TempPlaceObj.transform.position = WorldPos;
 
                 if(Input.GetMouseButtonDown(0)) {
 
                     Instantiate(TempInst, TempPlaceObj.transform.position, new Quaternion(0, 0, 0, 0));
                     
                 }
 
                 if(Input.GetMouseButtonDown(1) && hitplc.collider.tag == "Block") {
                     
                     GameObject.Destroy(hitplc.collider.gameObject);
                     
                 }
             }
             else
             {
 
                 TempPlaceObj.SetActive(false);
 
             }
         }
         else
         {
             
             TempPlaceObj.SetActive(false);
             
         }