You should add some more possible masteries because exhaust is a little redundant given that you already have Seismic Shard, especially for your guide since you max it early.

Pretty solid tank build, flat cd runes are pretty useless on malphite without clarity go for /lvl cd runes if you want cd

and why deadliness ?

Have only used this build once so far, but I went 5/2/9 before the other team surrendered. Thumbs up!

*edit*

Just played a second game and went 8/5/21. Best build for Malphite I've used.

I've recently started trying a few new things, trading Warmog for Soul Shroud / Spirit Visage, wich syncs with more coldown reduction and is much cheaper, and playing with HP quints, seems solid for now, i'll edit.

Hi Dotter! Thanks for the comment. Maybe you're right about the runes, I may try it later. Relative to the early "squishy" aspect, I ment in comparisson to the later game when you will probably be the thoughest champion in game. Maybe I should rephrase. Thanks again!

Hi. Quite similar to my build. However, I disagree that Malphite is squishy early game. He is able to harras and to be harassed a lot early game, which make him really annoying.
I wouldn't go with attack speed runes, as he won't do that much damage with a tanky item build. Get some armor, health or magic resistance instead. CD Reduction might be good because of the shard, but you can't use it that much early without clarity.
I do like the idea of the build, I guess I just have another way of playing. +1 from me :)