What parts do I need to complete just the frame(i.e. beaver tail, plunger, trigger, what pins, ect.)?
#1 A good, clear exploded drawing showing all the parts.
#2 Instructions (printed)
Aguila Blanca gave a pretty good list, but left off "Grips", which you are going to need.
The first thing you need to do is decide what kind of gun you are going to assemble. (and while I realize that "build" is the popular term in use, you are not really building a gun, you are assembling one.)
There are two basic types of 1911A1. The "stock" GI pattern (and spec) gun, the same as was used in WWII, and then there is "everything else".
When you ..build.. a GI spec gun, with GI spec parts, no fitting will be needed. The gun will function, and be minute of man accurate (at the least). When you use anything else, all bets are off.
Today, we have literally dozens of 1911A1 parts makers. Some are GI spec, some are not. Some claim to be, and are not. If not, that's where fitting will be needed.
Special tools are needed to install the plunger tube, grip screw bushings, and front sight (in the GI gun) The ejector is press fitted to the frame in the original GI gun. Replacement ejectors are held in place with a retaining pin, for which the frame must be drilled.
Current civilian frames come in different "flavors", and if you get one with the ejector, plunger tube, and grip screw bushings already installed, you will be better off.
If you are going to build a gun from the supply of aftermarket parts available today, it's pretty much a given some fitting will be needed. There is a learning curve to that, and you are starting at the bottom, so be prepared.
Do some more research, not knowing what you don't know is a bigger handicap than knowing what you don't know.
And just FYI, the "beavertail" is not a part. It is a style of a part, the grip safety.
Good Luck, and we're here to answer any questions we can.