My first question about blocks and prefabs

Hello community!

Im a guy coming from the Source-Engine mapping. This days im making my first beginner-steps in unity and i hope for the future, that you guys can help me out with a few questions?

So my question is: When i mapped back in Source-Times (Valve) then we built the map with something called "solids". These were simple blocks made of polygons. They could have different shapes like spheres and so on. When we wanted to add details to the map such like chairs, cranes, cars and so on, then we had something called "props". They pretty much worked like prefabs like in unity. My question is now: Are these prefabs made with blocks like in unity? Or is there a general difference between prefabs made of unity-blocks and imported 3D-Models? I think a compley prefab made of blocks in unity would pretty much slow down the game. Is my fear of that irrational? It would be nice if someone could tell me when to use 3D-Models and when to use the "solids" from Unity directly.

Thanks in advance.

 

So im going to be good, making the models by myself with meshes, because its gonna be a verly litte project. I would like to thank you for your answer.