Code copied from https://www.youtube.com/watch?v=Y1vURbU4WdU

Blocks.cs

using UnityEngine;
using System.Collections;

public class Blocks : MonoBehaviour
{
	
	//Public variable for the size of the terrain, width and heigth
	public Vector2 Size = new Vector2( 20 , 20 );
	
	//Height multiplies the final noise output
	public float Height = 10.0f;
	
	//This divides the noise frequency
	public float NoiseSize = 10.0f;
	
	private GameObject root;

	
	void OnGUI ()
	{
		
		//Make a button that generates when you press it
		if(GUI.Button( new Rect( 10, 10, 100, 30 ), "Generate" ))
		{
			
			//Generate!
			Generate();

		}
		
	}
	
	//Function that inputs the position and spits out a float value based on the perlin noise
	public float PerlinNoise(float x, float y)
	{
		//Generate a value from the given position, position is divided to make the noise more frequent.
		float noise = Mathf.PerlinNoise( x / NoiseSize, y / NoiseSize );
		
		//Return the noise value
		return noise * Height;
		
	}
	
	//Call this function to generate the terrain
	void Generate ()
	{
		
		//If we find a gameobject called terrain, there's a high
		//chance that we have the previous terrain still there
		//So, let's delete it
		Destroy(GameObject.Find("Terrain"));

		
		//Create a new empty gameobject that will store all the objects spawned for extra neatness
		root = new GameObject("Terrain");
		
		//Put the root object at the center of the boxes
		root.transform.position = new Vector3( Size.x/2, 0, Size.y/2 );
		
		//For loop for x-axis
		for(int i = 0; i <= Size.x; i++)
		{
			
			//For loop for z-axis
			for(int p = 0; p <= Size.y; p++)
			{
				
				GameObject box = GameObject.CreatePrimitive(PrimitiveType.Cube);
				
				box.transform.position = new Vector3( i, PerlinNoise( i, p ), p);
				box.transform.parent = root.transform;
				
			}
			
		}
					
		//Move the root at the origin.
		root.transform.position = Vector3.zero;
	
	}
}