I've used the roof surfacer a few times and it worked fine. If you are getting an error message maybe try spliting the surfaces up into smaller more manageable pieces.
And,
I am guessing that you have made a mesh form
and wish to have roof surfacer apply it to a roof.
If this is true then I believe you are in for some
GDL work to modify the roof surfacer to call
the Mass object made from the mesh form.
You need to study how roof surfacer works
with the existing roof surface objects to understand
how to get it to work with your roof surface object.
Peter Devlin
Nothing will bog down your project quite like roof surfacing! Well, maybe trees would give them a good run for their money! Hide their layer as much as is practicable I say!