Don't get me wrong, there are many really good settlement videos out there. It's just that most of them are somehow focused on building sizes and stuff, rather than be fully realistic. I'm talking about small details like missing pillars on tall buildings or bridges, or even spamming with duplicated fences, floors, etc. It's fine, this is a game after all.
I finished Fallout 4 couple of times and started focusing on my own settlements in detail. There are few I gave my full devotion. I started from Sanctuary Hills and worked there about a month. Then, to take a break, I switched to Red Rocket Truck Stop. After I finished Red Rocket, I decided to systematically build every settlement slowly, each time a quest sent me to it. We'll be referencing the most complete.