Buy Black Cleaver on Tanks?

As a top lane tank, it might be good to buy Black Cleaver first instead of Sunfire.

Galio and Gragas can afford to build Sunfire first because they also have ranged AoE abilities to poke and clear waves. But anyone who lacks that important strength was greatly nerfed by the sunfire changes.

Sunfire may cost 100g less than Cleaver, but it's far less gold efficient due to the lack of CDR. (the cost of 20% CDR is very near the actual cost difference when you factor in efficiency)