Champion.gg
I don't know how many of you guys know about this. I know how everyone refers to mobafire, lolking, solomid, etc. for guides and builds. But this site is also a great alternative and not only gives common builds for champs in Plat and above but also their highest wr builds, highest wr runes, masteries, starting items, and more. It even offers in depth champion matchups, counters, compliments, etc. The only thing it lacks are guides as it's mainly a culmination of statistics but I think it's pretty neat and I'd definitely recommend checking this out :)
^^^ link above ^^^