I usually put two stores in a 32W straight CC building, but I decided to build a "big" post office that would fill the entire available area. The interor is removable, works kinda like an oversized vignette.
The lady is about to send a postcard. The gent in the background is checking out his P.O. box.
The other side of the counter.
The sorting area.
The vignette is inserted in the building.
There is a small observatory on the top of the roof.