What is a 80% Lower Receiver

Is a FFL required to/build a firearm for personal use?

No. You are building the firearm for yourself for your own personal use which is legal under the Gun Control Act of 1968. This is on the ATF’s website under their FAQ page. You can see it here http://www.atf.gov/firearms/faq/firearms-technology.html .

 It is not required to be transferred through a Federal Firearms License Dealer with all the federal paperwork like its finished counterpart, the completely finished lower receiver.  These factors make for easy purchasing for home gunsmiths and hobbyists for personal use.

As long as the following laws are met there are no problems:

1. You can legally own the firearm in question in the state in which you live
2. You are building the firearm for your personal use and for yourself only.

It is a good idea to mark your firearm somehow so that should it ever be lost or stolen you have a way to identify it and report its loss to your local law enforcement. Please check your local and state laws.