I put one together for a guy about a year ago. Had an Olympic Arms matching flat top upper and lower. Put on a Hogue pistol grip. Front end had a "customized" 8 inch barrel. What that really means is that we chopped down a full size 16" G I Barrel that the guy had, per his request, and attached a Yankee Hill Machine muzzle break. Got a YHM front end, a full floated tube design that was, I think, about 5" long. Drilled the front end and attached a flip up, fold down front site, the back was the same, but it attached to the flat top rail.
We got a special piece that went between the lower and the buffer tube assembly, like the alignment washer on a stock assembly - but smaller, that gave him a single point of contact for a sling.
All in all, it was okay - nothing special. Guy probably spent more money than he got fun or accuracy out of it, but to each his own....