Alright, this is a pretty easy song. I think I got all the chords right, but I'm no expert.
it sounds good to me. Play it in standard tuning for the piano version.
and there's another version he plays with Capo 2. 
Let me know if it's wrong somewhere. Enjoy!

Verse 1:
      F       G               C
Well Gosh, I just think your swell
  F              G           C           Am
You could be my Heaven, when I feel like Hell
  F          G         C
Maybe we'll go for a ride
 F                G       C           Am
That's not a metaphor, I mean on our bikes
   F     G            C
Please, just hear me out


Chorus:

  Am       Em           F               C         F             G           C
Love it or leave it, I just can't stop dreaming about you all day and all night
    Am                 Em       F                  C
My friends think I'm crazy, but I don't think I'm crazy
   F            G           Am
I just have to find out and see
      F           G                    C
Katy Perry could you fall in love with me?

Verse 2:
     F        G               C
Well holy cow i think you're great
  F                 G        C             Am
I take you out for ice cream on our first date
     F               G               C
Well they all might judge you, you see?
    F                G          C          Am
But they don't know you, well neither does me
    F          G        C               Am
But if I knew you, I wouldn't judge you then
        F      Am          G             
Cause friends don't judge friends, ya know, just listennnnn


Chorus


Verse 3
     F                G             C
Well I don't have too many dollar bills
    F             G             C      Am
But i won't play cheap with my hea-aa-arrt.
     F                G                 C
It might be lame to sing your songs to you
          F         G            C                Am
But who knows, it might be what charms your pants off, wait
    F              G              C
I'm not trying to get your pants off
    F                G         C       Am
I'm just-well it's a figure of spee-ee-eech
  F         G                C
Maybe I'll charm your socks off
         F         G               C    Am
Do you think that might be more appropriate?
        G
Never mind, just listen to meeeeeeeee

 
Chorus