You are about to walk through some dangerous territory. I don't believe you need a FFL to make a gun for YOURSELF, but if the BATFE even thinks you are planning on selling it, or doing anything illegal with it, you could end up serving a very long sentence in Federal prison. I think they may also limit how many you can make per year (limited to one???). You are also going to need some very good machining skills, and some very precise equipment.
I recommend buying an 80% reciever if you really want to build one yourself. It will be much easier to finish, and will probably save you money.