Add an aircon or a few on the sideos of the building.
Add a starway up(just a box with a door, non acsess(or just add a door where it fits)).
Add a aircon for the building in general on the roo top.
You could add a stelite dich and a BIG tv antenne.
You could add a chimny or well you know what i mean.
You could add normal airwents.
You could add an advert holder or something.
You could make a shed out of scrap metal. add a matress and such for a hobo.
You could add a small table and some sun chairs.
Tell me if you need more ideas