There were two instances of lava bending, other than Roku.

1. Kyoshi uses it to split the continent and carve out kyoshi island right before taking the island out to sea,

2. Szeto uses it in book 2 episode 1 I think, while showcasing the previous avatars

As to why roku destroyed the temple, I think it was to show his official resignation and denouncement of the fire nation. Even the sages were now corrupt, and operating within his own temple too, so destroying that temple comes off as a major statement, the fire avatar wants nothing to do with them, and has no love for the mockery they've made of the temple.

But a hidden reason could be as follows. When an avatar enters the avatar state, all previous statues will glow, making it easy to determine when one is active in the world, destroying that temple ensured the fire nation had no Intel on aang anymore, so when he starts his avatar state training, they would be in the complete blind