Singed is a harass and annoy type fighter. Early game you just run in and run out, do circles through minion waves and escape when you need to, and toss enemies in the most useful fashion.By mid game his natural toughness starts to take over and you can stand and fight more.By late game it should take most of a team and some stuns to kill him.If you really have to run his adhesive and emergency defensive use of ulti should make him faster than anyone else, if they still chase that's even better.You should get lots of assist early and a few kills, then mid to late game the kills should start to stack up too.To be honest everything after rylia's is situational, archangel's and stacked deathcaps is usually a good bet though, or manamune if they have high magic resist.If you go the ad route I would suggest phantom dancer and infinity edge to round it out.