How do you guys handle building structures? It seems to be doing them modular might make more sense in case you want different interior variations between buildings, but how are they normally handled?
Thanks!
Both ways are used. The big advantage of modular building is, that you can have a pretty good variation but of course you will have to plan your assets carefully. But when you just want to use one building all over the map, you can also create the entire building in your 3d program. 
https://forums.unrealengine/showthread.php?25420-Model-Whole-Thing-or-Modular-Approach
Thanks so much. The presentation in that post you linked was great.
A building needs to be split up to some degree–each mesh only gets a single lightmap, so there’s that and also it doesn’t have to render things that aren’t visible, if everything is a single mesh then it can’t unload it.