Starcraft 2 has a very powerful map editor. You can add custom units for a map.

The big drawback to a starcraft map is you have to run it inside of starcraft with no standalone executable.

Thanks, I guess it could be useful for a prototype.

world generation, pathfinding, ai, building system and a resource system

your typical 3D engine will handle the pathfinding. world generation, AI, a building system, and a resource system are all game specific features. you may find some generic AI in some generic engines. you may find some of the game specific features in a similar game you can mod. but that would be about it.

Thanks for the reply. Do you know any games, which would fit my needs?

I would be able to do it myself, but I don't want to (if I can avoid it). :unsure:

Unreal does have a lot already built in, including path finding and AI... that's essentially what an engine is.

There's also a reasonable asset store with all sorts of 3D models and animations available.

Thanks, I'll take a look at it.

Sorry for the late reply, I was on vacation. :P

Thanks for the reply. Do you know any games, which would fit my needs?

Something like AOE or Warcraft, if they are mod-able. i would think that mod-able is the hard part, RTS's are a dime a dozen.