Maya or Unreal?

I build my assets in maya. But should I merge all the assets in maya or build my world in unreal… for example I have 50 buildings and the terrain. Do i put the building on the terrain in maya or do i build it in unreal… which one gives you a better sense of scale and which one is best?

You should place them in UE and try to reuse the same assets as much as possible. You could go even further by creating a Blueprint class that can switch between buildings.

You should use Unreal for better performances.
You can turn off unused meshes by distance, if you can try to use LODs.

Export all of them as separate files to not crumple performance as unreal in this case would load them as a single file, I recommend that you have each of one the models at the 0,0,0 translation of maya as unreal doesn’t take the pivot position from maya, but the distance from the center.

If you have already set up their positions in maya, you shoul add a placeholder box for each building that takes their translation, length and width as a reference to the final models in unreal, and export these boxes into a single .fbx without setting the translation as zero.

So to add my input…

You want to add them in Unreal because the lightmap baking process pretty much hates setups like the thing you’re suggesting in Maya. I’d look into the extensive and amazing Lightmapping documentation for more details on that. Because of that alone you won’t be able to save any draw calls by doing this and thus all performance benefits will be moot. Which leaves workflow aaaand… UE4 > Maya in regard to that for a few obvious reasons - Previsualization, sense of scale, world navigation, ect. are the obvious ones (:

Why is this Unreal Engine so inflexible and rigid?

Add each building individually to Unreal then setup lightmass importance volumes, LODs, and culling if applicable.