When I build architecture I tend to create the interiors first, and then conform the exteriors to the layout. Modular pieces are also the best route to go in my opinion, it may be a little time consuming to assemble depending on how you handle it but it’s worth it. You could separate the pieces and place the edge of each mesh along the origin in your modeling package. This would require careful planning for your pieces to snap together when put into UE4. Alternatively you can construct it in your modeling package, export it in it’s assembled location and set all of the mesh location values to the same value.