Draw a wireframe box with center and size.

	function OnDrawGizmosSelected () {
		// Draw a yellow cube at the transforms position
		Gizmos.color = Color.yellow;
		Gizmos.DrawWireCube (transform.position, Vector3 (1,1,1));
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnDrawGizmosSelected() {
        Gizmos.color = Color.yellow;
        Gizmos.DrawWireCube(transform.position, new Vector3(1, 1, 1));
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnDrawGizmosSelected() as void:
		Gizmos.color = Color.yellow
		Gizmos.DrawWireCube(transform.position, Vector3(1, 1, 1))