tools wise if you purchase a complete assembled upper and are just needing to assemble the lower then pretty much the only tool you will NEED is a pair of vice grips with some tape wrapped around the jaws, and a punch and rubber mallet will make a few things easier but you could get one together with just the vice grips in a pinch.
If your going to build your upper too then add an action vice and a barrel wrench to the tools needed.
Personally I don't think it's worth it to assemble your own upper unless you were going to be doing a LOT of them or are able to borrow the tools for it since they add quite a bit more cost to the project than the amount that they save. And it can all be shipped to your door.
Your basic parts that would be needed would be
Stripped lower reciever
Lower parts kit
buttstock/buffer/buffer spring
completed upper reciever.
I think on a seriously penny pinching build I could probably put one together for right around $540
T