Guardian Angel just after boots? I don't think it's a good idea. Sure, you have auto-resurrect, but 40% from your hp at this stage of the game is not enough to survive after resurrect in most situations. And its quite expensive items and i think other items would be much better.
I suggest thornmail when facing physical dmg team, which would be great, especially when combined with a defensive ball + taunt combo.

However Warmog should be bought earlier, because it takes time to charge it up.

I also suggest banshee's veil when facing magic dps team.

As a tank your role is not to die (anyway, it ofc happens), so i would change mastery points from "Good Hands" and "Ardor" (because it's a **** mastery for him in this build) to "Evasion" and "Nimbleness", to additional dodge/speed.


And what about your advices about tactic and at least short presentation of the advantages/disadvantages of this build?

Anyway, build is quite good, develop it a bit and i'll rate it positive.