To get round this, extra sets of doors on the 4819 fire station have to be set back (staggered), as can be seen in the first pic showing the fire station fitted with the 7465 add-on set. The second set of doors is about 10.5 cms behind the first set. If you're building a three bay station, the third set of doors is 31.5 cms behind the first set! For that reason, I prefer just to buy the parts needed to fit an extra set of doors flush with the original set - see second pic. It is realistic, works well and is cheaper. It looks a bit bare on top, but I'm sure there is a System-X piece or pieces which could be fitted to form a parapet or suggestion of a roof line.
The last pic is a scan of part of the fire and rescue page from the 2010 catalogue. As you can see, all the sets of doors are flush with each other and if you look closely you will see that they are not connected to each other because the roof structure doesn't allow this.