// Draws a window you can resize between 80px and 200px width
// Just click the box inside the window and move your mouse
private var windowRect : Rect = Rect (10, 10, 100, 100);
private var scaling : boolean = false;

function OnGUI () {
windowRect = GUILayout.Window (0, windowRect, ScalingWindow, "resizeable",
GUILayout.MinWidth(80), GUILayout.MaxWidth(200));
}

function ScalingWindow (windowID : int) {
GUILayout.Box("", GUILayout.Width(20), GUILayout.Height(20));
if (Event.current.type == EventType.MouseUp) {
scaling = false;
}
else if (Event.current.type == EventType.MouseDown &&
GUILayoutUtility.GetLastRect().Contains(Event.current.mousePosition)) {
scaling = true;
}

if (scaling) {
windowRect = Rect (windowRect.x, windowRect.y,
windowRect.width + Event.current.delta.x, windowRect.height + Event.current.delta.y);
}
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
private Rect windowRect = new Rect(10, 10, 100, 100);
private bool scaling = false;
void OnGUI() {
windowRect = GUILayout.Window(0, windowRect, ScalingWindow, "resizeable", GUILayout.MinWidth(80), GUILayout.MaxWidth(200));
}
void ScalingWindow(int windowID) {
GUILayout.Box("", GUILayout.Width(20), GUILayout.Height(20));
if (Event.current.type == EventType.MouseUp)
scaling = false;
else
if (Event.current.type == EventType.MouseDown && GUILayoutUtility.GetLastRect().Contains(Event.current.mousePosition))
scaling = true;

if (scaling)
windowRect = new Rect(windowRect.x, windowRect.y, windowRect.width + Event.current.delta.x, windowRect.height + Event.current.delta.y);

}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

private windowRect as Rect = Rect(10, 10, 100, 100)

private scaling as bool = false

def OnGUI():
windowRect = GUILayout.Window(0, windowRect, ScalingWindow, 'resizeable', GUILayout.MinWidth(80), GUILayout.MaxWidth(200))

def ScalingWindow(windowID as int):
GUILayout.Box('', GUILayout.Width(20), GUILayout.Height(20))
if Event.current.type == EventType.MouseUp:
scaling = false
elif (Event.current.type == EventType.MouseDown) and GUILayoutUtility.GetLastRect().Contains(Event.current.mousePosition):
scaling = true
if scaling:
windowRect = Rect(windowRect.x, windowRect.y, (windowRect.width + Event.current.delta.x), (windowRect.height + Event.current.delta.y))