Having read Canmore and other reports before the visit, I had expected to be underwhelmed by this site.
Comments like "has been much disturbed by secondary buildings and its present form bears little relationship to its original plan" do not raise expectations.
To my eyes, what you actually get is a well fairly well preserved Hebridean Passage Grave with a lintelled passage plus chamber with a few side stones still standing a most of the rest fallen into the chamber.
Any secondary building was limited to the outside cairn material and, reading the reports again after the visit, maybe that's what they meant.
But don't be put off. This is a site worth visiting especially if you've come to see Clettraval anyway.