Onslaught?
Class based base building survival gamemode.
You get and admin-set amount of build time to make a base. After that time is over you defend your base from either Combine, Antlions, or Zombies. Most maps have all 3 in different places
It's also class based. Engineers can build turrets and heal their props, scouts are fast, and there's a couple other classes I don't use.
There's also a money system for building props.
