Posted by deadin:
It's my understanding that if you build one from scratch, it's strictly for you, you can't transfer it to anyone else unless you have a manufacturers license.
As an individual you can build a legal gun (i.e. not FA, 922 compliant etc) and sell it at a later date to a third party. Below is an extract from a BATF&E letter on the subject. *
http://forums.impactguns.com/archive/index.php/t-335.html * This is dated 2004 but you will find that here are many such posts giving the same information.
-------------- Extract from BATF&E letter ----------
Also, for your information, a nonlicensee may manufacture a semiautomatic rifle for his or her own personal use. As long as the firearm remains in the custody of the person who manufactured it, the firearm need not be marked with a serial number or name and location of the manufacturer. However, if the firearm is transferred to another party at some point in the future, the firearm must be marked in accordance with the provisions set forth in 27 CFR § 478.92 (formerly 178.92).
------------- End of ectract -----------------------
You may (will) run into problems if you were to build an unreasonable number of such guns in any given year and subsequently sell them : a hobbyist cannot make "a full-time income" from selling guns be they home made or commercial. Even if (as a hobbyist / gun enthusiast) you were to "buy / trade and sell" commercially made guns and then sell a few of your items at gun shows you must not make sufficient income for it to be classified as being a full-time income: this is the province of the FFL who is expected to make such an income. The ATF will ask to see records of ALL transactions you have made to establish what income you have earned.
A PROVISO:
Like every BATF&E "regulation / rule / pray list / daily re-write list" this area is open to the particular ATF rep's mood and inclination at any given time ... but what else is new

The bottom line is yes you can make a gun and sell it - just don't make more money in a year than an out of work rabid squirrel hunter. And keep a written record of everything bought (inc. compliance parts and so on) and sold together with all costs incurred by yourself - preferably witnessed by the Pope or someone else of unimpeachable standing !!
Hope this info (it was also confirmed before posting by my FFL who works closely with the ATF and knows his onions) is of some value.
Best to all, and keep on fighting for our freedoms, Bbet.