I did one back in the fall of '12.... Ordered straight from the US. ITAR changed after Sandyhook..... 80% lowers are no longer exportable....
It took 4hrs to complete the lower. I used a drill press with a milling base @ work. Fairly easy process, if you are mechanically inclined (and you took Industrial Arts in High School).
According to the firearms tech I talked to, you have 30 days to register your lower after completion. I also learned that "all rules pertaining to storage and transport of a restricted firearm apply".... This means you will not be able to get authorization to take it to the range (ATT) until you have a copy of the cert, or a transfer document.... Which you cant get because you didn't transfer it....
It took 9 months to get my Cert.... I had to register it as a complete rifle, they would not let me register it as a "lower" only. They required pictures of the lower. Later on (read 8 weeks) they asked for pictures of the complete rifle. Later still (4weeks) they asked me to have a verifier fill out some paperwork on it.... Then later still they asked if I had "drawings", and could they get a copy....
Other than the "satisfaction" of building one, it is a MUCH more expensive option over buying a $200 completed mil-spec lower (ie: Aero Precision), let alone a $100 lower form one of our fine site sponsors....
I'm not saying it isn't worth doing..... It's just not cheaper, nor is it less hassle and it is a F*k Ton more work....
My $.02