I found a couple of versions of this song on UG, but neither were great.  One was 
really easy but sounded wrong and the other sounded right, but was really quite 
hard to play, so I've got a compromise.  

To play this song correctly, you'll need to tune your guitar down a half step.  

INTRO:
(think about the intro as being in 4/4 and eighth notes.  So, 1+2+3+4+ 1+2+3+4+ 1+2+3+4+ 1+2+3)

Eb|--10---10---10---10---10----10----10---10---10---10---10---10---10---10---10----|
Bb|-----8----8----8----8-----8-----8-----8----8----8----8----8----8----8----8------|
Gb|--------------------------------------------------------------------------------|
Db|--------------------------------------------------------------------------------|
Ab|--------------------------------------------------------------------------------|
Eb|--------------------------------------------------------------------------------|

{G D Em C} x2

G              D               Em                C
Don't you ever wonder what will happen when it ends? 
G              D         Em                     C
How can we let go of the ones who we call friends?


      G                D
And I know it's only a story
           Em                  C
But for so many it's more than that
       G                 D
It's a world all on it's own
                Em                   C
Where we want to put on that Sorting Hat

          D         Em        C
And I will miss the train ride in
        D           Em       C
And the pranks pulled by the twins
                D       Em     C
And though it's nowhere I have been
             Am
I'll keep on smiling
          D    Dsus2 (let ring)    G (listen to song for strum)
From the times I had... with them

{G D Em C} x2 

  G               D         Em             C
Could there ever be again another one like this?
G                   D
One, that's brought us together
       Em                      C
And started its own music movement



          D         Em        C
So I will miss the train ride in
        D           Em       C
And the pranks pulled by the twins
                D       Em     C
And though it's nowhere I have been
             Am
I'll keep on smiling
          D    Dsus2 (let ring)    G (listen to song for strum)
From the times I had... with them


{G D Em C} x2 


Em        C         G
Soon we will see it closed
   Em     C       G
The final chapter exposed
        Em        C       G
It's an end of an era and I'm seeing clearer
A                  C     
 Nothing will ever be the same


          D         Em        C
So I will miss the train ride in
        D           Em       C
And the pranks pulled by the twins
                D       Em     C
And though it's nowhere I have been
             Am
I'll keep on smiling
          D    Dsus2         G
From the times I had with them

{G D Em C} --repeat throughout last section (listen to song for changes)

From the times I had with them 
From the times I had with them
From the times I had with them
From the times I ha_____d with them
Oooh, From the times that we had
From the times I had with the_______m
From the ti__________mes I had with them
From the times I had with them
From the times we had with them
Oho, From the times we had with them
You and me, the time we had
The times we had with them
With them...

repeat C

    G             D                Em     D       Cadd9 
So don't you ever wonder what will happen when it ends..?