League of Legends (LoL) Question: AD Build and Tank Build???

For best items, it really depends on your champion. Their engage, cc, poke etc all effect this. However to carry, AD is the best, either full AD or bruiser build. Full tank allows your team to carry you and puts a lot of pressure on you. If your doing poorly in lane, build tank, at least for top which I assume you play comsidering the question. If you want to carry, and are winning lane, go damage and carry the other lanes!

Tank meta is everywhere.....
Tanks mean you have to depend on your team
AD means you know you can carry the team
I Usually go for a mix of both.
I Usually rush Tiamat on Jarvan into Titanic and Jungle item (or Dead man's if your top)

So if you want to carry a game, I would recommend going for AD, you still can carry as a tank but tanks are usually only strong at Early Game. But if you are playing high AD champions, a few kills and you can carry the whole team from Early to Late. Moreover, building will let you farm faster, so if both teams are having equal kills, more creeps mean more chance to carry your team.

About builds, it's very hard to tell which build is the best since each champion suits a different style, you can search on Mobafire or Champion.gg to find the best builds.