How does Epic set up the materials for their large structural meshes?

I’m trying to create the structure of a map in C4D to import into UE4 instead of using brushes, because it’s easier to manipulate the geometry. I managed to get the models within the Editor, but I cannot figure out how to set up the UVs. The models are large pieces that go up to 4000 units across in size. I can’t get enough resolution on a simple UV layout to cover it all with any sort of material.

I was taking a look at DM-Outpost, where Epic did the same thing: the whole structure of the map is made out of large models. But somehow, they made it so the materials are tileable when applied on the model. If you look at the picture I uploaded, which is of a piece from the outside area of the map, you’ll notice how there doesn’t seem to be anything on the UV layout (bottom left corner square). The only thing there is, I suppose, is a few selection groups on the model which they use to apply the materials.

How do I make that? I know how to set up selection tags in C4D, but how do I set the UV to tile the materials across the model like that?