I feel chord inversions really make or break this song. So here's how I play it.

Tempo around 47 bpm

Intro:
RH - D drones quarter notes throughout
LH - Bm5 - G5 - D5 - A5 (+ add4 with C# in RH) 

Verse:
All bass notes (LH) are in root position, but some chords (RH) are inverted.

D (root)
F#m (2nd inversion: C# - F# - A)
G (2nd inversion: B - D - G) +optional add9 in 3rd measure
D (root)
A (1st inversion: C# - E - A)

Chorus:
Similar to the intro, but full chords.

Bm (root)
G (2nd inversion: B - D - G)
D (root)
A (1st inversion: C# - E - A)




Bm5            G5                    D5                  A5
Say something, I'm giving up on you

Bm5         G5                     D5                     A5
I'll be the one, if you want me to

Bm5      G5                         D5                    A5
Anywhere I would've followed you

Bm5            G5                    D5                   A5
Say something, I'm giving up on you


    D                F#m
And I am feeling so small

       G
It was over my head

                      D             A
I know nothing at all


    D                  F#m
And I will stumble and fall

           G
I'm still learning to love

                       D                A
Just starting to crawl


Bm              G                      D                A
Say something, I'm giving up on you

Bm             G                      D                  A
I'm sorry that I couldn't get to you

Bm        G                      D                  A
Anywhere I would've followed you

Bm             G                       D               A
Say something, I'm giving up on you


    D                F#m
And I will swallow my pride

            G
You're the one that I love

                         D             A
And I'm saying goodbye


Bm             G                     D                A
Say something, I'm giving up on you

Bm                 G                    D                A
And I'm sorry that I couldn't get to you

Bm           G                      D       A
And anywhere I would've followed you (Oh-oh-oh-oh)

Bm             G                      D                 A
Say something, I'm giving up on you


Bm5           G5                     D5                A5
Say something, I'm giving up on you

Bm5            G5                  D5
Say something...