are you seeing a lot of revives yet?
if not, darius, kassadin, teemo, kha and jayce are really solid picks.
if yes, scrap darius because people are getting used to countering darius once you get a relatively high level, but he still shines against bad comps or having great cc supports.
if you want to support a bit more: alistar, lulu and sona make great hybrid support/damage champs.
hextech sweeper, grez lantern and lightbringer are some of the most op items because they allow you to facecheck and gains vision of targets so they can't juke you through bushes or fog and they have incredibly cost-effective stats (e.g. for just 200 extra gold on sweeper, you get 10% movement speed, anti-shrooms, the active which is really good and on top of the small bonuses like +100 HP and +10 AP)
if taking back windmill is real hard, some of you should try ganking their bottom laner if their 4 top are at the windmill area, but not all 4 of you because at least 2 or 3 should defend your mid in case 4 of them decide to charge at your mid.
if you want to get arpen, usually most skilled players that I see skip cleaver and go brutalizer+last whisper instead because cleaver needs 5 stacks to be fully effective and the cost of brutalizer+last whisper is roughly 3637 gold just 637 gold above cleaver but grants the high arpen permanently without the needing to apply stacks first.