Handles.DrawWireCube

Нарисуйте коробку с center и size.

using UnityEditor;
using UnityEngine;
using System.Collections;

//this class should exist somewhere in your project
public class WireCubeExample : MonoBehaviour
{
    public Vector3 size;

    // ...other code...
}

// Editor script. This would go into an Editor directory.
using UnityEditor;
using UnityEngine;

[CustomEditor(typeof(WireCubeExample))]
public class WireBoxExample : Editor
{
    void OnSceneGUI()
    {
        Handles.color = Color.yellow;
        WireCubeExample myObj = (WireCubeExample)target;
        Handles.DrawWireCube(myObj.transform.position, myObj.size);
    }
}