Spoiler'd for your convenience
"Ground level" of the Tower of Oranges (Click for unnecessarily large version):
I've got drawbridge entrances at the top and bottom, with barracks and dining rooms for the two squads that guard those entrances. Far right is the barracks for my marksdwarves, with a firing range upstairs. Top right and bottom left are towers for sieges (I've still got to do the top left and bottom right). Central building is a tower in progress (it's only about 4 stories tall so far) and houses the central staircase of the fortress. It's also got drawbridges that I can pull up to keep nasties out in case the walls get breached.
Haven't bothered screenshotting the subterranean levels yet, but I've got farms, some empty rooms dug out for cave trees to grow, workshop and storage levels, a main dining hall & kitchens, water drawn from the river for wells in addition to a nice waterfall decontamination shower just before the dining hall (the drainage tunnel is completely covered in blood), bedrooms deeper down, and way down I've got magma furnaces and forges cranking out steel armor and weapons for the military.
Ohhh, that's nice. What's the hotkey for screenshotting a full z-level?
Also, did you dig a trench under your drawbridge?
Without a trench, that drawbridge can be destroyed easily by enemy invasions...
Nope, drawbridges aren't affected by building destroyers. Only dorfs can remove them (or magma, if they're not magma safe), hence making them THÉ safest doors in the game. Of course, there is the risk of crushing people (which is good), and they have a slight delay on input from levers (which is not good), but i go with bridges all day. Hell, they can do most things that doors and hatches can, and you don't need a workshop to make them.