I built my own using all Colt parts. My cousin built one and used what ever he could find quick and ended up with a rifle that had 5 different companies names on it when he was done and it did not shoot for ****. I would stick with one brand if i were you just to be on the safe side.
Then he probably screwed up the build or used the wrong parts for the particular style (ex. carbine, rifle). Most of the parts (even Colt) are made by a small handful of companies and are all interchangeable, but rifle and carbine parts aren't necessirly compatible.