Your grade seems to be based on overall presentation which is definitely not something most first builds go for. They want rating based on performance which im sure you've yet to test. As far as optional items go, I don't believe there should be any for the situation because this build itself is not for each situation. If ur deal with about 3 AP users than that alone should tell u not to build AD. I'm not looking to adapt simply cause with the right strategy you can do fine in most situations. The only ones that dont demand a whole different build altogether. Now I will consider making it however i do not intend to make anymore time for it at this time.

So first off i dont like the idea of spliting runes ever, i know some people like to go 5 and 4 with some runes or 2 and 1 with the quints but really all you do is get very small buffs that only hurt you late game. Secondly I would like to see more information on items and possible optional items for various situations. As you said you hadnt seen an AD build for him so this gives lots of room to work with, dont be afraid to go all out and give us all the information you can. Thirdly, the use of BBcodeing is always helpful (i dont downvote just on lack of BBcodeing but it something i see a lot of first builds missing).

Positively, I do like the build you use and the concept, I have played AD Malphite in the past and it can be very fun (although it is somewhat situational). Sounds like a solid champion idea.

Finally This guide should help you out with codeing and making it better overall.Jhoijhoi's Making a Guide
Feel free to PM me if you change and fix some stuff and I will look at changing my vote to a positive vote.

+1 rep me if it helped