Converting void OnGUI to my own buttons I make... PLEASE HELP!

Here is my script:

 using UnityEngine;
 
 public class SelectUsername : MonoBehaviour
 {
     public static int userNumber = -1; //current user (<=0 means nothing selected)
     public static string userName = "";
     string[] usernames;
     int numUsers = 0;
     
     // Start is called before the first frame update
     void Start()
     {
         //Get the player names in the array usernames at Start
         numUsers = PlayerPrefs.GetInt("NumUsers", 0); // how many registered users?
         usernames = new string[numUsers + 1]; //create user name list...
         for (int n = 1; n <= numUsers; n++)
         {
             usernames[n] = PlayerPrefs.GetString("User" + n); // ...and load them.
         }
     }
 
     // Update is called once per frame
     //Below is all AUTO CREATED, which I do NOT like, but it works. I want to make my OWN buttons.
     void OnGUI()
     {
         if (userNumber < 0) //if any number isn't defined yet do the following
         {
             Rect r = new Rect(300, 300, 300, 100);  // create basic rectangle
             GUI.Label(r, "Select User");
             for (int n = 1; n <= numUsers; n++)
             {
                 r.y += 100;  // offset rect to the next line
                 if (GUI.Button(r, usernames[n]))
                 {
                     // if user selected...
                     userNumber = n;  // save number...
                     userName = usernames[n];
                 }
             }
         }
     }
 }

I want to replace the auto button maker list of void OnGUI with buttons I make myself. Can someone PLEASE help me? I also do NOT want to use prefab buttons either.