Sunfire is bad on singed because he's not going to be sitting around in a teamfight, standing around next to the other team.
You're focusing on tank with this build. Fine. Good. But why are you going Boots of Swiftness instead of Mercury's Treads, then?
Rylai's Crystal Scepter is core on singed. A 6 second slow that makes you that much faster is amazing.
Your lack of levels in your slow disturbs me. You say you're not focusing on damage in the guide, yet you're neglecting higher CC for more damage... that isn't even going to be that much more damage anyway, since you have very little AP. You don't build your philosopher's stone into Shurelya's Battlesong, which is a pretty good item on singed.
Your marks are very disagreeable.
Your masteries are... well they're bad. You don't need 0-21-9, especially with this build. Your 9 points in utility are so messed up... Perseverance is a **** mastery. It literally does nothing. But you neglect your exp gain mastery to get it.
There's a lot of weird things I'm seeing on your build. I didn't downvote, I want to hear what you're going to say.

Also, hearing your playstyle tips, I strongly disagree. Hugging tower till they're close enough to get flinged into the turret is not worth letting them get farmed, and getting your lane pushed.
Another thing: You talk about running in case of trouble. That's all good fun, but as a tank, sometimes you just HAVE to lay down your life intentionally, to give your carry a better chance to escape. It's something I learned from tanking a long time; especially as Alistar.