Mine are straight shaft down, right to the bottom
Third from bottom is bedrooms, second from bottom is food and dining rooms, bottom is tombs
First soil layer is workshops, all shops are in lines of 7 in a 11x4 room
farms are either on first or second soil, are farms are separate 5x5
all layers below are mines.
What Really sets mine apart from the forts I've seen is the layout.
All my levels are made of 4 3x3 tunnels going north,south, east, west. all straight.
most other people's forts are also more open inside, like greathalls and such. I NEVER do that.
My current fortress, Weaverwalls, is a lot like that. It's a big tower with eight 5x5 rooms each floor (plus a space in the middle for storage and stairs), not square since the diagonal rooms are closer to the center and the cardinal direction rooms are pushed further out so they all have their own doors facing the center. This basic design goes all the way to the bottom, including lava and water layers (with a protected inner core for the stairs of course), and it so happens the bottom floor is the main coffin complex.
Every major tunnel is at least 3 tiles wide, I find it easiest to design around and big enough to handle traffic. The main idea with Weaverwalls was it'd be this natural stone tower with sides exposed to the outside, with all the stone around it carved out wider and wider the farther you get from the tower. Or removed entirely to leave the tower the tallest thing on the map (I think the mountain ended up about 3 Z levels shorter, total). Since I wasn't sure how far I'd dig down, all the early mining was done from the bottom of the map, with tunnels in each cardinal direction traveling a bit out, then traveling up once they got far enough away from the tower.
This substantially increased the trip of course, since my smelters had to travel about 12 Z levels down, about 50 squares south, then 14 Z levels up -- before they were even on the same plane as the magnetite veins! this was an unusual fortress for me though. I would like to make more open great halls and courtyards, I just rarely do. The closest I get to that is outside defense-works or protected groves of trees / outside farm plots.
My normal designs have 3-wide or 5-wide hallways, that would surround a 11x11 square grid that could be either 4 5x5 rooms or two 5x11 or whatever suits the purpose of the rooms. Every workshop I make is in at least a 5x5 room, which gives space for clutter or stockpiles. Nearly everything is located on the same Z-level, which I feel makes pathing simpler and much less laggy, as well as making it simpler to watch my dwarves. Water, magma, mechanical systems, and other little details such as roads and defense towers have to be on different Z levels by necessity though.