Had left the item build intentionally unfinished, specifically so people wouldn't simply skim over it without reading the logic behind the choices, but I'll put in the other items I suppose. Shame there's no "X Or Y" option for the items list.

As for the runes... well, I'm sorry but your math is wrong. At level six, mp5/level runes are the same as, or better than, flat mana regen. Glyphs for example - 0.055*6=0.33 each, whereas the flat ones are only 0.31 for the entire game. MP5/level Seals are very slightly less effective at six, being 0.065*6=0.39 versus 0.41 flat MP5, but the difference is minimal. Kayle is mana hungry at all levels, having less than a thousand base mana and only around 10mp5 at level 18. Yes, it's slightly worse at early game since you have no items, but you need to consider the entire game; if you're too reliant on the golem buff for mana regen, you aren't giving it to your carries.

On the Meki Pendant versus a Doran's Ring... to be really honest I switch between the two fairly frequently depending on the enemy team. If you go the Meki route like I show in the build, you just need to play a little cautiously for the first few levels. Kayle's got a pretty poor early game, and rather than try to kill an inferno with a bucket, I find accepting her poor performance and playing around it means you get your items faster and are better mid and late game for your team.

Voted.

While i understand why you are taking Meki for your first item, Kayle is way to squishy early game to take advantage of it. While I wouldn't recommend taking two Doran's Rings, like my Guide says (currently revamping it). A Doran's Ring gives Kayle that little extra HP and AP to survive in lane so she can level up and start her support. Also it might help your guide if you completed your item build up top. Most people don't bother to read that you mention a FoN and Thorn Mail.

I've tried this kind of set-up for Kayle plenty.
I don't feel your build has addressed her early game mana-hunger at all. It's the main reason why Kayle's hard to play.

Clarity runes don't have much effect during the levels 1~10, and Codex isn't quite enough imo.
Early Meki Pendant also leaves her a tad squishy with no power early game.