This build is for the balance type of player that likes to play a balanced hero that can stay in the lane as long as possible. This build is also good for mid since you can heal and regain mana slowly then own your enemy. Also don't spam your spells. Only use them if you have a good amount of mana. If your mana is getting low where you can only use one spell, you should just stand back and let your mana and health regain slowly then use your heal. Flash and Ghost are there to get you out of bad situations. Also ghost can be used when you see an ally about to die, just rush to them and ult them or heal then run back. Ghost and Flash are great when you're at one bar of life and your enemy is tower diving. Your W also gives you speed so you can run fast and bait him around the tower.

For marks I went magic penetration since I am a fan of spamming Q which does a good amount of damage.
For seals I went evasion because I noticed that you evade more often with them so when you're fighting or running away it helps. Also there aren't really any helpful seals for Kayle.
For Glyphs I went for the cooldown reduction which helps max our the CD reduction so you don't need to golem. It gets it up to 39%, you can swap one of the glyphs if you want to the 0.9 one if you want max CD reduction. It's at 39. something so it'll max out. But I don't really see it neccessary, I think it is max not sure.
For Quints I went ability power since Kayles passive is dependant on Ability power and attack damage. The magic penetration would only increase it by four, so why not take the ability power +14 or whatever ability power. It'll increase your damage as well and your ability since damage gets converted to AP as well.

Well Nashors tooth and Guinsoo is a necessary on Kayle. I'm not sure about the hextech gunblade but since Kayle is a hybrid it seems right to get it. I usually skip that and go for the last two items. But eh I'm going to try it and see how it goes. I like to play the Kayle that can heal herself and her team when pushing so that..when the enemy engages and retreats..the next time they attack, you'll be able to heal your entire team back up to full health. I have done this so I know it's possible to heal your entire team while you push. Also sell the dorans ring when you're at your last item. It's useful throughout the game cause of the mana regen, AP, and health but by 14 you won't need it.

I usually get Q and W maxed out. Of course I get R whenever I'm the level for it. E I get last only because I like using Q to slow and beating them down with my sword and just healing through the damage they deal to me. E I get last only because I like to play support and heal my team mates and myself. Q is also awesome because you slow people a lot and they're usually dead in a gank or even a 1v1.

Of course these are used for running and chasing. W also speeds Kayle up so you run even faster. This is for escape, kiting, chasing, and mainly surviving situation.

Kayle is a great hero. She's a great support to the team with her ult and heal that can save a teammate from being killed. She is not a carry in the sense that she'll kill the entire team, but is a healer that can keep the team from being killed and at full life. Play her however you want but do not engage in 2v1 battles. If you get into those, just use summoner spells or ult away and heal.