what I am doing wrong here?
Nothing wrong, just read my first signature.
The Weighted Straight Skeleton algorithm compute holes in the roof projection NOT in the roof face.
Accordingly to the hint, the difference for the extra point could be less than 1 cm which, in real world of the house constructors, it's not a big deal.
Probably you want something like this:
The plugin interface:
Probably you (and others users) have to wait.
If all roll normally this will be a gift for this Christmas.
It's a work in progress (a lot of work [:(] ) and noting push as (GRT) to be hurry!