I'm looking around here and there for more information on what other parts / tools do I need to acquire before I put the finishing touches on Armalite AR15 Clone.
However I am not having such luck as been looking at guides and technical menu's; there is no need to mention brand names, just the part or equipment that I am missing to finish my build.

Things I have :

Lower Receiver
Complete Upper Receiver ( http://www.thefirearmblog.com/blog/2015/02/24/colt-canada-iur-integrated-upper-receiver-civilian-sale/ )
Lower Parts Kit
Magazine for ammo
Roll Pin Starter / Finisher Set
Ear Plugs

Things I know I don't have yet:

Charging Handle
Scope
Buttstock Kit or Buffer Tube
What's a Castle Ring?
Lube (We all need that at some point in life)

Thanks for the help

A castle nut is what holds the extension tube in place,  you will need as castle nut wrench, I prefer Tapco's $9 castle nut wrench.

Otherwise the stuff you need is about it, probably want a non marring hammer too, and masking tape to cover things while you work. I also like a lower vise block but its not necessary.

stripped upper
upper parts kit
charging handle
BCG
gas block
gas tube
barrel
hand guard
muzzle break
stripped lower
lower parts kit
grip (if not included in lower parts kit)
trigger (if not included in lower parts kit)
lower tube kit
stock


Save optics for last.

Depending on if you will be using a sling, you may want a sling attachment ring (end plate) QD or other to go on before the castle nut. All depends on how/if you attach a sling. I only mention this because I forgot to get mine before my build and had to wait a long painstaking week for it to arrive.

When buying the receiver extension (the other name for a buffer tube) and buffer, pay attention to the buffer weight. Make sure you have the correct weight buffer for your gas system; a carbine buffer might not be so good in a rifle length gas system, and vice a versa. Also, pay attention to the stock and buffer tube to make sure they are either both commercial spec or both mil spec, you do not want to mix and match here.

This. And not just this but the proper size buffer as well. I've been at the range before and a guy couldn't figure out why his newly built AR was whacking his shoulder so hard and yet not stripping rounds from the mag. Turns out that since he had a rifle length gas system that he put a rifle buffer in it. Normally not a big deal, unless you are like him and put it all into a mil-spec tube with a 6-position adjustable stock. The rifle buffers are significantly longer than the carbine buffers (which you can easily see while holding both) and aren't interchangeable if you have an adjustable stock due to the buffer tube being shorter.