1. I am unsure whether he really did mend the roof.
  2. I am unsure whether he really mended the roof.
    Do they mean the same?

Hi Allifathima,

Personally, I doubt I would ever use ‘mend the roof’. The verb ‘repair’, for example, would be more typical.

As for the form of the verb itself (did mend vs mended), the use of ‘did mend’ is more emphatic. You might use this form if someone had just stated that he had successfully fixed/repaired/mended the roof and you then wanted to emphasize your doubt that that was true, for example.

[size=75]“Forgiveness is the needle that knows how to mend.” ~ Jewel[/size]