I added planes for floor and ceiling and booleaned a long box from the right wall to make a long window, I used box primitives to make small window frames.

I've cut and extrude the walls to define the hallways. This is how it looks like from the inside and from the outside (Fig. 08 & 09).



I used cylinder primitives for the water pipes in the far right corner of the room, and box primitives for the acoustic ceiling; editable spline was used for the ceiling frame (Fig.10).



 I cut, rotated and deleted some of the ceiling plates and added electricity pipelines made from renderable splines. With editable poly I cut the wall corners for some damage details. Tip: you can add temporary omni lights inside the room which make it easier to see things in the view port, whilst working on things inside the room - just make sure you don't forget to delete them when you start working on the final lighting  (Fig.11-12).

Modelling the fan

For the cage of the fan, I started with a chamfer cylinder (Fig.13), and added an "Affect Region” modifier to blow it up a little (Fig.14)