Array question

So i have a array that will continuously add buildings every time the player places a building. So how would I set it up to take money from the same script and decrease it by a certain amount every time a building is placed. Please help me

here is my script for reference c#

using UnityEngine;
using System.Collections;
    
public class Game : MonoBehaviour {

	
	public int defaultMoney = 100;
	public int minMoney = 0;
	public int maxMoney = 20000;
	public string moneySign = "$";
	//*************************
	public Object[] buildings = {};
	private int buildingCount;
	public Object[] buildingsuz = {};
	private int buildingCountuz;
	public Object[] buildingsuo = {};
	private int buildingCountuo;
	//*************************
	public GUIContent content;
	public Texture2D building1;
	public Texture2D building2;
	public Texture2D skyScraper;
	public Texture2D gvcc;
	public Texture2D courtHouse;
	public Texture2D powerStation;
	public Texture2D road;
	//*************************
	public bool isNormalSpeed;
	
	// Use this for initialization
	void Start () {
		
		building1 = Resources.Load("Building1") as Texture2D;
		building2 = Resources.Load("Building2") as Texture2D;
		skyScraper = Resources.Load("SkyScraper") as Texture2D;
		gvcc = Resources.Load("gvcc") as Texture2D;
		courtHouse = Resources.Load("CourtHouse") as Texture2D;
		powerStation = Resources.Load("PowerStation") as Texture2D;
		road = Resources.Load ("Road") as Texture2D;
		
		InvokeRepeating("CountUp", 5, 5);
		
	}
	
	void CountUp(){
		
		foreach(Object item in buildingsuz)
		{
			defaultMoney += 10;
		}
		foreach(Object item in buildingsuo)
		{
			defaultMoney += 30;
		}
		
	}
	
	// Update is called once per frame
	void Update () {

		if (maxMoney <= minMoney) {
			
			Application.Quit ();
			
		}


		buildings = GameObject.FindGameObjectsWithTag ("Building");
		buildingCount = buildings.Length;
		buildingsuz= GameObject.FindGameObjectsWithTag ("Buildinguz");
		buildingCountuz = buildingsuz.Length;
		buildingsuo= GameObject.FindGameObjectsWithTag ("Buildinguo");
		buildingCountuo = buildingsuo.Length;
		
		if (defaultMoney >= maxMoney) {
			
			defaultMoney = maxMoney;
			
		}
		else if (defaultMoney <= minMoney) {
			
			defaultMoney = maxMoney;
			
		}
		Debug.Log ("What is normal Speed at: " + isNormalSpeed);
		
	}
	
	
	void OnGUI(){

		int w = Screen.width, h = Screen.height;
		
		GUIStyle style = new GUIStyle();

		Rect rect = new Rect(0, 0, w, h * 2 / 100);
		style.alignment = TextAnchor.UpperLeft;
		style.fontSize = h * 5 / 100;
		style.normal.textColor = new Color (1.0f, 1.0f, 1.0f, 1.0f);
		string text = string.Format("Money:" + moneySign + defaultMoney);
		GUI.Label(rect, text, style);
		
		GUI.TextArea (new Rect (740, 10, 100, 30), "Buildings: " + buildingCount);

		if (Input.GetKey (KeyCode.B)) {
			
			GUI.Box (new Rect (10, 50, 200, 200), "Buildings");
			GUI.skin.button.normal.background = building1;
			GUI.skin.button.hover.background = building1;
			GUI.skin.button.active.background = building1;
			if (GUI.Button (new Rect (20, 70, 50, 50), "")) {
				
			}
			GUI.skin.button.normal.background = building2;
			GUI.skin.button.hover.background = building2;
			GUI.skin.button.active.background = building2;
			if (GUI.Button (new Rect (80, 70, 50, 50), "")) {
				
			}
			GUI.skin.button.normal.background = skyScraper;
			GUI.skin.button.hover.background = skyScraper;
			GUI.skin.button.active.background = skyScraper;
			if (GUI.Button (new Rect (140, 70, 50, 50), "")) {
				
			}
			GUI.skin.button.normal.background = gvcc;
			GUI.skin.button.hover.background = gvcc;
			GUI.skin.button.active.background = gvcc;
			if (GUI.Button (new Rect (20, 140, 50, 50), "")) {
				
			}
			GUI.skin.button.normal.background = courtHouse;
			GUI.skin.button.hover.background = courtHouse;
			GUI.skin.button.active.background = courtHouse;
			if (GUI.Button (new Rect (80, 140, 50, 50), "")) {
				
			}

			GUI.skin.button.normal.background = powerStation;
			GUI.skin.button.hover.background = powerStation;
			GUI.skin.button.active.background = powerStation;
			if (GUI.Button (new Rect (140, 140, 50, 50), "")) {
				
			}
		}

		if (Input.GetKey (KeyCode.M)) {
			
			GUI.Box (new Rect (635, 50, 200, 200), "miscellaneous");
			GUI.skin.button.normal.background = road;
			GUI.skin.button.hover.background = road;
			GUI.skin.button.active.background = road;
			if (GUI.Button (new Rect (645, 70, 50, 50), "")) {
				
			}
		}

		if (Input.GetKey (KeyCode.E)) {
				
			GUI.Box (new Rect (400, 40, 100, 100), "Road Options");
			if (GUI.Toggle (new Rect (410, 60, 50, 50), false, "Left")) {
					
			}
			if (GUI.Toggle (new Rect (410, 90, 50, 50), false, "Right")) {
				
			}
			if (GUI.Toggle (new Rect (410, 120, 90, 90), false, "Intersection")) {
				
			}
		}

		if (Input.GetKey (KeyCode.U)) {
			
			GUI.Button (new Rect (400, 40, 100, 50), "Buildings with Upgrade Zero: " + buildingCountuz);
			GUI.TextArea (new Rect (400, 80, 100, 50), "Buildings with Upgrade One: " + buildingCountuo);
				
		}
	}

	void FixedUpdate(){

		if (Input.GetKeyDown (KeyCode.P)) {
			
			if(isNormalSpeed == true){
				
				Time.timeScale = 2.0f;
				isNormalSpeed = false;
				
			}
			else if(isNormalSpeed == false){

				Time.timeScale = 1.0f;
				isNormalSpeed = true;
			}
			
		}


	}
	
}

Add a variable to represent your current money. Set it to defaultMoney at Awake or Start. Create a function to handle payment (“Pay” in example). Call Pay() when you want to buy a building.

int money;

void Awake()
{
    money = defaultMoney;
}

// Return true if payment was successful.
// Return false if didn't have enough money.
// Trows ArgumentException if amount is negative.
bool Pay(int amount)
{
    if (amount < 0)
        throw new System.ArgumentException("Can't pay negative amount", "amount");

    if (money - amount < 0)
        return false;

    money -= amount;
    return true;
}

Example usage:

        GUI.skin.button.normal.background = powerStation;
        GUI.skin.button.hover.background = powerStation;
        GUI.skin.button.active.background = powerStation;
        if (GUI.Button(new Rect(140, 140, 50, 50), ""))
        {
            if (Pay(50))
            {
                // Create power station building.
            }
        }