I have a 2006 Goose Neck in the same 727 sunlite, I love mine I bought it brand new and  had the back enclosed and a living quarter added in 2010, I am very pleased with my trailer.

The 2005 Sundowner 727 would be a steel framed aluminum skinned trailer.  The issues were frame related with these models if they were from the areas of the country where salt or calcium chloride was used during winter months.  If these trailers were used in the winter, and not taken care of, they could have frame issues.  I would say that either have someone inspect the trailer for you, or get a good set of pictures of the underside of the trailer.

As far as the roof, Sundowner only uses one piece aluminum roods; no fiberglass roofs. 

The 727 will make you a good trailer; once you have checked out the frame situation.