Buy a quality rifle / carbine and don't try to build one. In the classes that I have been to approximately 90%+ of the "built" guns have gone tit's up.
I think that the key part of this statement is "in the classes that I have been to..." That percentage can't be that high world-wide; I believe that it would be ALOT lower. It would be interesting to find out why those 90% failed, though. Bad parts and/or workmanship would be my guess.


Mega Gator complete lower receiver with M4 adjustable stock.
AFAIK, Mega doesn't make stocks or LPKs. Yet, anyway. All I've seen from them are stripped receivers and charging handles so far. Question the brand of components that they're using. Mega receivers are very good, but a deal isn't a very good one if you have to put up with bad internal parts. Good luck!