Hut circles vary greatly. Don't be fooled by Stonelifter's promise of masonry. Lots of them look earthen:

http://www.themodernantiquarian.com/post/32730

That's not to say that the stonework isn't buried underneath.

Also, there's a fine line between hut circles and hut platforms. The latter is where a shelf has been cut into a hillside on which to build a hut (often visible within the fortifications of hillforts).

K x