Instantiate working in Awake but on in Update

So I have a list of gameobjects, the list is linked to some UI elements through which I can click to decide which gameobject I want to create. To try out this code I wrote a simple timer in my update to create the object selected in my UI elemet every 3 seconds.

activeBuilding is the var that the list adjusts to decide which building to instantiate

When I call the instantiate line in Awake it works fine (with the list number assigned directly in the code to activeBuilding). However, when I try the same thing in Update it gives me an "Argumentoutofrangeexpection: argument is out of range".

Im not sure what I am doing wrong here, please let me know if you need any more information to help me out! This is my code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Buildings : MonoBehaviour {
 
     private int BuildingType;
     private int BuildingGroup;
 
     public List<GameObject> BuildingList;
 
     private int activeBuilding = 3;
 
     private float time = 0;
 
     public void selectBuilding(int index)
     {
         activeBuilding = index;     
     }
     private void Awake()
     {
         selectBuilding(0);
     }
     public void BuildingCreation()
     {
     }
     private void Start () {
         BuildingList = new List<GameObject>();
     }
     public void Update () {
 
         selectBuilding(activeBuilding);
 
         time += Time.deltaTime;
 
         if (time > 3)
         {
             Debug.Log("active building = " + activeBuilding);
             Instantiate(BuildingList[activeBuilding], new Vector3(10, 01, 10), Quaternion.identity);
             time = 0;
         }
     }
 }