what is singed's main source of damage?
his poison trail that does dot damage/aoe damage
build
and he will do a lot less damage to you...
singed isnt trying to kill and fight... he is trying to out cs and push lanes hence the proxy singed strategy ... he is gonna use Q and run between your turrets and farm the wave between them before they have a chance to make it into lane. or do this in your base.
by out csing and wave clearing him you force him into lane to protect his turrets. otherwise he loses them and you gain map pressure and control . and gold for team. which makes you ahead.
and when he is between your turrets you need to coordinate with team ( and ward ) to trap him and you + jungler and/or with mid all kill him push lanes/waves and objectives
this is how you beat him.
nasus is a good pick vs him cuz you want to passive sit and farm and stack Q ... so with him doing his proxy thing you get to last hit for free
plz before you cry over something being toxic/cancer etc learn the game