"Has anyone ever built an ar15 without ever owning one first?"
If you have some patience a few minor tools, can watch videos and follow the instructions, you can do it.
That said, I would opt for a completed upper. Not that you and I can't put it together but with out the 'block' to hold the upper receiver while torquing...
The lower isn't that much of a problem. It does take three hands when putting pins and detents in the stripped lower (watch out for flying pins and springs).
Building, putting it together is more correct, 'it' yourself is very satisfying and gives 'you' a working understanding of just what is inside.
From your question I must determine that you don't have an AR. Remember that ARs run better 'wet'. I use Mobile One on my bolt carriers, wet with it. After a couple of shots, the excess will be blown away.