I have lots of netherrock sitting in my inventory and I want to build some structures with it. Just wondering if I would have to weatherproof them, given that netherrack burns indefinitely, or if it behaves like cobblestone in this aspect and I don't have to worry about lightning.
The fire generated from lightning is the same as any other fire source.
However, since fire will not destroy netherrack, nor does fire on netherrack spread to other netherrack blocks, there is no trouble in letting them burn indefinitely (though most of them will be put out by the rain anyway).
In short, as long as you don't mind the possibility of rooftops randomly on fire, there's nothing much to worry about.
Netherrack will burn if hit by lightning, and will continue burning indefinitely. When lightning strikes an object in minecraft (other than water/lava) it will catch on fire.
To prove this, I did an experiment:
I then used a function in zombe's modpack which allows me to manipulate lightning at a specific location.
As expected, the netherrack lit up. In the end, I used lightning on every single netherrack block I placed, and they burned indefinitely. The result: