I have an idea: A story about a giant sized monster going around destroying a massive city and the military are trying to kill it. This idea was inspired by Kaiju movies. I plan to come up with my own monster for this story instead of using an already existing movie character. What do you think about this idea?
It's been done before. You would have to come up with a way to make this really original. You would also need to really do research to make sure the destruction and military response are believable.
You also need an actual story. What you've described is a situation, not a story. A story usually has a specific protagonist that wants something and tries to overcome obstacles to get it. You need to ask yourself what story this scenario would allow you to tell.
It's a Kaiju story. That's what it is. There's nothing more to it. That's not really an idea, it's just describing all Kaiju stories. If you want to write it, try to make it be something that hasn't been done before.