Not sure about the original key but this is how I play it:

C (x32010@1) Am7 (x02010@1)     Dm7   GI'm (320003@1)singin' in the rain
Just singin' in the rain
What a glorious feelin'
    Dm (xx0231@1)   G7I'm (320001@1)happy again
    Dm7          G7 (320001@1)       Dm7     G7 (320001@1)I'm laughin' at clouds, so dark up above
    Dm7         G7 (320001@1)           C (x32010@1)        GThe (320003@1)sun's in my heart and I'm ready for love

C (x32010@1)  Am7 (x02010@1)    Dm7    GLet (320003@1)the stormy clouds chase
Everyone from the place
Come on with the rain
       Dm (xx0231@1)         G7I've (320001@1)a smile on my face
   Dm7           G7 (320001@1)        Dm7     G7I (320001@1)walk down the lane with a happy refrain
      Dm7           G7 (320001@1)           CJust (x32010@1)dancinin' and singin' in the rain