Insert a flexible space element.

Flexible spaces use up any leftover space in a layout.

Note: This will override the GUILayout.ExpandWidth and GUILayout.ExpandHeight

Flexible Space in a GUILayout Area.

	var sliderValue : float = 1.0;
	function OnGUI() {
		// Wrap everything in the designated GUI Area
		GUILayout.BeginArea (Rect (0,0,200,60));
		// Begin the singular Horizontal Group
		GUILayout.BeginHorizontal();
		// Place a Button normally
		GUILayout.RepeatButton ("A button with\ntwo lines");
		// Place a space between the button and the vertical area
		// so it fits the whole area
		GUILayout.FlexibleSpace();
		// Arrange two more Controls vertically beside the Button
		GUILayout.BeginVertical();	
		GUILayout.Box("Value:" + Mathf.Round(sliderValue));
		sliderValue = GUILayout.HorizontalSlider (sliderValue, 0.0, 10);
		// End the Groups and Area
		GUILayout.EndVertical();
		GUILayout.EndHorizontal();
		GUILayout.EndArea();
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public float sliderValue = 1.0F;
    void OnGUI() {
        GUILayout.BeginArea(new Rect(0, 0, 200, 60));
        GUILayout.BeginHorizontal();
        GUILayout.RepeatButton("A button with\ntwo lines");
        GUILayout.FlexibleSpace();
        GUILayout.BeginVertical();
        GUILayout.Box("Value:" + Mathf.Round(sliderValue));
        sliderValue = GUILayout.HorizontalSlider(sliderValue, 0.0F, 10);
        GUILayout.EndVertical();
        GUILayout.EndHorizontal();
        GUILayout.EndArea();
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public sliderValue as float = 1.0F

	def OnGUI() as void:
		GUILayout.BeginArea(Rect(0, 0, 200, 60))
		GUILayout.BeginHorizontal()
		GUILayout.RepeatButton('A button with\ntwo lines')
		GUILayout.FlexibleSpace()
		GUILayout.BeginVertical()
		GUILayout.Box(('Value:' + Mathf.Round(sliderValue)))
		sliderValue = GUILayout.HorizontalSlider(sliderValue, 0.0F, 10)
		GUILayout.EndVertical()
		GUILayout.EndHorizontal()
		GUILayout.EndArea()