Thanks Andy!

To make the windows it is just grabbing faces and extruding them inwards, The main thing is planning all the placement of them first when building the main shape.
Getting all the edges that will make up the frames of the windows in the right place is the most important thing at that stage, I use the grid in a front view (or side view depending what side I'm working on) to measure out how many edges will be needed for the windows, making sure they are all spaced out equally, or at least where they are supposed to be!
The main thing is to get the overall shape of the building in there first, then keep refining the detail, adding more as you go, as is the case with all modelling really!

Hope that does help somehow, best of luck in your projects too!