@agneesh
I checked out your model. Although the roof geometry has been categorized correctly as a “Roof” in Revit, because the geometry is custom and has not been created by Revit, it does not adopt some of the charactaristics and behaviours of Native Roof object. Therefore you can not attach a Native Wall to a DirectShape roof. One alternative is to create a flat roof using the boundarya and then use the Revit API, to add internal points to the roof and raise them to the appropriate elevations.