I was in the same boat b/w a build and buy and I had never even handled an AR before and still haven't shot anyone else other than mine.
You could build a Daniel Defense rifle but change the furniture on it to Magpul stuff and save some weight and money right off the bat while having a MOA rifle.
For my first AR I decided to go with a build and had no idea where to start. I couldn't even tell you what half the parts were, where they were supposed to go or why I should choose what over what.
Your lower won't matter much since there are 4 main companies that make lowers and stamp someone else name on them. I went with MEGA, ultimately giving me a real nice tight finish b/w the upper and lower. Google search will brink up what brands fall under what manufacturer.
Most importantly invest your money in a 1:7 Chrome lined barrel and a quality Bolt Carrier Group.