It's not. Building for your ultimate solely is a mistake. Build for strong Q's, that's where most of your utility comes from. Hitting their backline midgame with a rank 5 Q and a couple items will devastate them. Running around mid game with boots 1, dorans ring, and hat will allow anyone to sneeze on you and you will die.

This is pretty optimal item build orde in ca 80% of the games. There are plenty of exceptions tho when you will want to change build order (talon/zed/veigar/fizz/lb etc.) and even build other items first.
When it comes to skills yes depending what you are going for you can level Q over W later depending what you prefer. I prefer to be able to bring really strong mid game ganks so W+R and add E+ignite is pretty much kill on anyone.

It's not a guide. It's a build. A very general build that doesn't explain anything about the champion. I could make a build as specific as this for every champion in a day. Get more specific.

Everything above (except the skilling order) is fine, the guide is not bad written. you still have to improve it but its not bad

Boots 1, dorans ring, rabadons? Strongly disagree
Max W second? strongly disagree
Rylais/Liandrys? disagree
Scaling MR runes? nope

I'm not convinced this is nearly optimal