I've seen several threads that have shown things like floorplans for various common buildings like multi-story residential homes.
Around the time I did that raw-editable procedural worldgen city thread, someone else was drawing out a couple dozen different generic buildings over in the Fortress Mode Forum. Someone did a "elf tree" thread about a month ago, and it was only "flamed" (term used very lightly) because the guy had the elves using forges "because Tolkein did it".
(As a total side note, you don't really need a floor plan for a ziggurat - a ziggurat was just a raised platform like a pyramid with the top half of it cut off, and other buildings like the marketplace and temples built on top of the artificial hill. Ziggurats aren't what they are in the common misconception.)
Anyway, if you want to take a shot at some types of buildings you want to make that are odd enough to be something Toady possibly hasn't thought of yet, then go ahead and take a crack at it. Just keep in mind that he's probably thought of the basic stuff, and you'd probably do better to come up with good reasons to come up with unusual types of buildings.
So basically, look at the stuff he already has for humans, for example, and try to come up with buldings that should be there, which should be shaped differently, and try to go for why, or at least why some sort of cultural trait should make it look different in another culture.
Hell, I haven't seen much of anything on goblins - you could probably do something on dark towers to make them more livable, or make their functioning make more sense fairly easily.