Ok theres this kid named [SA]Brian and he just randomly spawned a huge skyscraper right when i was making an airplane. i worked over 1 hour on it and was not done and hadn't duped. He then placed the skyscraper on top of my airplane and the collisions must have crashed the server.

It shouldn't be up to me to say it, but
1. Proof?
2. ID?

Well, I can imagine that it would be difficult to take a screen, if it crashed moments after he spawned it. Same with ID.

But yeah. Hard to do anything without the two.

Server dont log all steam ids of people that join?

Sure, but that probably wouldn't provide proof. You could see the props spawned.. Can't you?

There is function to find people you recently played with, i find it very useful, but for the screenshot, try to take it if you see him before the server crashes.
You know he could have hit print screen when he saw the guy spawning a sky scrapper and tell him self, i gotta report this guy

Just sounded like the crash happened a few seconds after he spawned it. At least to me.