Selecting Object From Top Causes NullReference

This is a very odd situation I am faced with here. I've been working on an RTS style selection, with the help of a tutorial from YouTube, for a game I am working on with a friend. I've never created a building placement and selection system before so off to Google and YouTube I went. Anyhow, a result I didn't expect has arisen. In it's simplest form, clicking one of the sides of a cube placed down, selects it as expected. However clicking the top of the cube returns a NullReferenceException.

I am totally baffled, I have googled the issue with no luck, I've even attached the debugger from MonoDevelop to the Unity editor so I can step through the code and see what's going on. That hasn't helped me narrow it down either. Below you will find a couple screenshots, and the code.

As you can see in the image above, the cube has been selected via one of the sides, it is selected properly, no errors.

And now, the image above shows the cube being selected from the top, however it returns a NullReferenceException. Below is the entire source code (well the relevant scripts at least)

BuildingPlacement.cs

 using UnityEngine;
 using System.Collections;
 
 public class BuildingPlacement : MonoBehaviour {
 
     private PlaceableBuilding placeableBuilding;
     private Transform currentBuilding;
     private bool hasPlaced = false;
 
     public LayerMask buildingsMask;
     public PlaceableBuilding placeableBuildingOld;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         Vector3 m = Input.mousePosition;
         m = new Vector3(m.x,m.y,transform.position.y);
         Vector3 p = camera.ScreenToWorldPoint(m);
         
         if(currentBuilding != null && !hasPlaced) {
             currentBuilding.position = new Vector3(p.x,0,p.z);
 
             if(Input.GetMouseButtonDown(0)) {
                 if(IsLegalPosition()) {
                     hasPlaced = true;
                 }
             }
         }
         else {
             if(Input.GetMouseButtonDown(0)) {
                 RaycastHit hit = new RaycastHit();
                 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                 Debug.DrawRay(ray.origin, ray.direction * 100, Color.red, 15);
 
                 if(Physics.Raycast(ray, out hit, Mathf.Infinity,buildingsMask)) {
                     if(placeableBuildingOld != null) {
                         placeableBuildingOld.SetSelected(false);
                     }
                     hit.collider.gameObject.GetComponent<PlaceableBuilding>().SetSelected(true);
                     placeableBuildingOld = hit.collider.gameObject.GetComponent<PlaceableBuilding>();
                 }
                 else {
                     if(placeableBuildingOld != null) {
                         placeableBuildingOld.SetSelected(false);
                     }
                 }
             }
         }
     }
 
     bool IsLegalPosition() {
         if(placeableBuilding.colliders.Count > 0) {
             Debug.Log("Cannot place building(s), too close!");
             return false;
         }
         else {
             return true;
         }
     }
 
     public void SetItem(GameObject b) {
         hasPlaced = false;
         currentBuilding = ((GameObject)Instantiate(b)).transform;
         placeableBuilding = currentBuilding.GetComponent<PlaceableBuilding>();
     }
 }

The only relevant piece of code from this next script is the SetSelected function

PlaceableBuilding.cs

     public void SetSelected(bool s) {
         isSelected = s;
     }
 }
 

The line of interest in the NullReferenceException is this one:

 hit.collider.gameObject.GetComponent<PlaceableBuilding>().SetSelected(true);

I am totally stumped on this. Any and all help is deeply appreciated.

   Debug.Log(hit.collider.name + ", " + hit.collider.tag);