What is an efficient way to somewhat closely model a real life building?


I live I an old catholic school which was repurposed into an apartment building, and I think the building has an interesting design which I would like to replicate in a 3D model. I want the model to be something I can use in a game engine and add textures to in order to make it look similar to the real building.

Just to give a bit of an idea of what I am working with - it has two sections that are perpendicular to each other. One section (Section A) has a basement floor and 3 floors above it. The other section (Section B) has 2 floors, but its ground level floor is adjacent to the other section’s basement floor. Section B’s ground floor connects to Section A’s basement, and Section B’s 2nd floor connects to Section A’s 1st floor.

I have been wanting to do this since I moved in about 2 years ago, but each time I approach it, the task seems much too daunting to attempt. I just don’t know the best place to start for modeling buildings. I have tried starting by modeling the outside of the building, then working in, but it seems impossible to get the interior to match up to the outside dimensions. I have tried only modeling the floor planes of each of the hallway interiors as closely as possible to the real measurements, then working up from there, but it still somehow gets off.

I am not looking to model it perfectly down to the inch - I just want it to resemble the building closely enough to give a similar feeling. What would be a common workflow to begin to approach a task like this?