What program did you make the model in? You are going to need to UV map the whole thing for Unreal, and split it into different sections for better light mapping. Here’s a link to the documentation that helps you do it:
The process is pretty simple in 3ds Max if you have done it before, but if you’re model is in Revit or something like that your are going to have to export it as a .fbx file and import it into Maya or Max to UV map. Personally, I have had trouble with this process of Revit to unreal, but others have had success. I think one guy used Navisworks to break the model up and UV map, but I may have that wrong.
The other issue with large scenes is that it takes forever to build the lighting in engine. There has been all sorts of research around the lightmass in UE, and if you read this thread you can get some great tips on it:
Lets make Lightmass EPIC (and understandable) - Architectural and Design Visualization - Unreal Engine Forums
For me, using custom values in the engine’s lightmass code, it takes about four to five hours to build a pretty small scene, but for larger models it can take a really long time. I recommend you read up on this before trying to build the lighting as if you mess up, you have to sit through it again.
This is mainly the hard stuff about archviz in UE4, but you can get good results if you know what you’re doing. Be sure to read the forums here and other places on the web. The UE4 documentation also provides to be a relatively useful source, in fact here is one on lighting and realistic rendering:
Oh, and one more thing. Because you haven’t done any work in unreal before, download the “Berlin Flat Demo” by xoio in the marketplace (its free) and take a look at all the components. Look in the architecture folder and see how they unwrapped the UV’s for each of the walls and components, especially notice the two channel system that is used by Unreal. This provides a great basis for learning how to make a nice scene.