Two big ticket Armor items, but no MR aside from the merc treads until after both those AND a TF? It's true that armor is more often the primary damage type, but it's rarely wise to build only one defense.
I would put an Abyssal Scepter or a Force of Nature in place of Randuin's. The scepter gives you and your team more damage while FoN boasts much more MR, Health regen, and some nice bonus movespeed. I tend to go AS if there mages aren't bothering me much and FoN if they're being problematic.
Going for CDR is the right idea, and I'm trying to work TF into my build as well but so far don't have a solid slot for it. Even if I can't finish it, the Sheen proc is nice on her Q and Phage is always useful.
We start off similar, but instead of two gems I just build the Kindlegem right away, boots, and one of each pot. I'm rarely low on health in the first fight, either dead or doing fine. That's why I take the mana pot, because if the fight goes on for a long while I find myself short on mana.
Every now and then I think about how maybe I should use FH instead of Randuin's Omen as my main Armor item, but ultimately I stick with Randuin's. I reason that, as much as I want the CDR, Randuin's gives me health. I don't like only having a kindlegem/upgrade as my single Health item, considering that I only buy Phage late game.
And lets not forget Randuin's whopping 5% CDR! 8D
As far as runes/masteries, I go 9/21/0 with Mpen in the Offensive tree. I figure the pre-requisite CDR mastery and the mpen together are worth more to me than the bonus AS and ArPen of the other masteries. Likewise, Mpen marks, but tanky everything else.
As far as rating your build... I'm bad at throwing down solid numbers like that. I think there are ups and downs of both our builds, best I can do is to show mine for comparison and tweaking.