My main halls and corridors are built for functionality. 3 square wide hallways with alleys leading off them to workshops and rooms. Once I get a fort established I make a throne room for the baron. usually with pillars of stone lining the procession in a hallways 4-5 levels high. With a throne made in the most expensive materials I have available. Plus a second one beside it if he/she has a partner. If I want to get really fancy I add balconies halfway up the rooms sides with chairs designated as meeting halls for the commonfolk to watch their ruler meet dignitaries.
Otherwise rectangles and squares seem to be common themes foe my fort layouts and architecture. Usually organised around one or two main stairways 3x3 wide. With very centralized areas for industries. With one main floor (usually under the caverns ) for food processing and production. And different crafts getting their own quarters of the fort. Like the stonemasons quarter, The woodorker and tailors quarter, The metalworking quarter. With a trade depot being not far from the singular entrance all my forts have for easy access. Usually with my main warehouse stockpiles beside it.
Bedrooms. I have dedicated housing levels usually spread around 3-5 floors after the first few years. Containing extra food storage for finished food. Legendary dining halls, wells and bedrooms. Every dwarf gets a 3x5 room with bed, cabinet, coffer and door. With nobles getting extremely decadent quarters verging on mini fiefdoms in their own right. Usually I end up making an arena with a labyrinth under that deep in my fort to throw prisoners to beasts Iv'e caught. I once had a cyclops roaming around my Labyrinth that regularly slaughtered the naked goblins thrown to it. I liked to imagine it was how the dwarfs of the fort made sacrifices to their deities.