I just assembled a lower yesterday with only basic tools. here are some helpful hints.
trigger/disconnector: put the trigger into the receiver and then put in a receiver pin into one side and line up the hole with the hole in the trigger and push the pin until it is flush with the inner area of the trigger assembly but not sticking into the area where the disconnector will go. Do the same with the other pin on the other side. Now the trigger is in place and you can focus on getting the disconnector lined up without worrying where the trigger is.
hammer assembly: dont worry about breaking anything. These springs are very tough. wear safety glasses during this process to protect your eyes should the assembly fly out. Place the ends of the spring on the trigger pin on opposite sides of the trigger assembly. push down and forward until the holes are lined up. having another person hold the hammer in place while you put the pin in is VERY helpful.
Roll pins: Dont hit the pins themselves with a hammer, have punches to use with these pins. If you dont have punches you can improvise with any metal rod of good strength and proper size. IMO you want the rod to be slightly larger than the pin to keep the rod from sliding off while hammering.
TIP: using a resin covered hammer can help prevent scratching the receiver.
pivot pin dentent/spring: If you dont have the installation tool then dont fret. put in the spring and then the detent. Then push in and hold with something thin like a nail file. anything hard that wont get in the way of the pivot pin. Then put in the pivot pin with the groove AWAY from the spring/detent. once the pin is a fair ways in then turn it around and line up the groove in the pin with the detent.
Note: The pivot pin sometimes needs a break in. This involves lubricationg the pin and the holes and pushing the pin in and out several times. a hammer and punch comes in handy here.
thats all for now cuase Ive got a headache but more may come later.
The only thing I could add to this thread with my limited knowledge of assembling a stripper Lower would be to second the use of safety glasses. God only gave you one pair of eyes.
One more would be to use Tetra Grease on the inside of the various trigger and hammer pin holes and the corresponding components plus the front and rear takedown pins. Alittle goes along way and makes everything go together as smooth as snot.
This has been said before, but when installing the pivot pin detent/spring PUT THE RECIEVER IN A PLASTIC BAG. This will keep the detent from flying of to who-knows-where. I lost the detent yesterday and would be Very Sad today if I didn't have a spare in my spare parts kit. I would also say to break in not only the pivot pins, but also the bolt catch. Mine wouldn't tip up enough to catch the bolt and after reading the troubleshooting section I was worried that I might have installed the wrong spring. I lubed it real well with Tetra Gun Lube (which, I have to say, I really like), worked the catch a few dozen times and it works fine now.
If thinking about buildng your AR, all I can say is DO IT! It didn't take me long at all and the pleasure of knowing you took a bunch of parts and turned them into the rifle YOU wanted can't be beat.