How to prevent overlapping GameObjects before instantiation

I have created a basic 2D dungeon generator script that lays down rooms in a random offset direction from the last placed room. I am struggling to come up with a way to check if there is already a room spawned in the place where a new room will spawn. Right now the rooms will go back on themselves and create large blobs of overlapping rooms, like this example with 2000 rooms generated:

I have looked into different options on implementing some sort of ray casting solution where before I spawn the room I shoot a ray in the direction to check if there is a pre-existing room there and if there is it will choose a new direction. I confused of how I would implement this and any help would be appreciated. Here is the code that I am working with:

 using UnityEngine;
 using System.Collections;
 
 public class Generator : MonoBehaviour {
 
     //set up Gm's for generation
     public GameObject roomBlock;
     GameObject room;
     //set the number of rooms that will spawn in total
     public int numRooms = 8;
 
     float posx, posy, posz = 0;
 
     int randDirection;
 
     Quaternion rotation = Quaternion.Euler(270, 0, 0);
 
     void Start()
     {
         
         //Generation should only run through once at the start
         Generate(numRooms, roomBlock);
 
     }
 
     void Generate(int nrms, GameObject roomBlock)
     {
 
         //create the starting room at coords 0,0,0
         room = (GameObject)Instantiate(roomBlock, new Vector3(posx, posy, posz), rotation);
 
         //subtract 1 room from room pool
         nrms--;
 
 
         for (int i = 0; i < nrms; i++)
         {
             //get xyz of last spawned room
             posx = room.transform.position.x;
             posy = room.transform.position.y;
             posz = room.transform.position.z;
 
             //choose random direction (NSEW)
             randDirection = Random.Range(0, 4);
 
             //based on randomized direction spawn a room
             //spawn room in same position as last room but offset by 1 in the randomized direction
             if (randDirection == 0)
             {
                 room = (GameObject)Instantiate(roomBlock, new Vector3(posx + 1, posy, posz), rotation);
             }
             else if (randDirection == 1)
             {
                 room = (GameObject)Instantiate(roomBlock, new Vector3(posx, posy + 1, posz), rotation);
             }
             else if (randDirection == 2)
             {
                 room = (GameObject)Instantiate(roomBlock, new Vector3(posx - 1, posy, posz), rotation);
             }
             else if (randDirection == 3)
             {
                 room = (GameObject)Instantiate(roomBlock, new Vector3(posx, posy - 1, posz), rotation);
             }
 
 
         }
         
     }
 
 }