Robert - We have a client set up like this. They have two buildings next to each other, primary office in building 1 on level 27 and secondary office in building 2 on level 30.
Both buildings have windows that face each other, so we set up a ZF7731 bridge on some heavy duty speaker stands in each window with around 60 meters distance between.
This is being used for their primary link which they run all their data across plus a set of ZoneDirector 3000's with 14 x ZF7982s in their primary building and 3 x ZF7982s in their secondary building.