Dear Binoj,

No, You can not define the Pivot line of the roof tool different from a straight line. Nevertheless, you can use this trick:
-Define your pivot line with an auxiliary spline or arc segments. I'm supposing that by pivot line you mean the base of the roof.
-Use "snap points" and set it to either divisions or distance. this will be the length of the roof's pivot segments.

If you have a very weird shape on the roof, try with it first with the Mesh tool, and then create a roof form that mesh.

I hope this helps.

Cheers

Nando