Remember the chase through that really big hall in Moria during LOTR? The one with pillars everywhere? Like that. It's the method I use for my dining halls, but you could theoretically do it for an entire fortress.
Pause. Start by selecting your top level, make it one tile wider in all dimensions than your lowest-level floorplan. Plot out a dig around the perimeter, a one tile wide tunnel all the way around the edge, keeping in mind the size of column you want to use (I normally use 3x3, but for this sort of project I'd recommend 5x5, I'll get to why in a bit) and the distance you want between columns, such that you end up with a total floorplan which divides neatly. Follow by designating one-tile digs around every column. Connect the columns with each other and with the rim using whatever pattern of tunnels you want--I prefer one-tile wide from the center of every column ring to every adjacent column and wall.
Once you've got that entire plan mapped out, copy the dig down through every z-level you want the fortress to occupy. After that, unpause and designate an access tunnel for the top level. Once it's all mined out, smooth everything. After everything is smoothed, designate every tile of black space within the floor plan (which isn't a column) for channelling, not including the one-tile tunnels you've smoothed. Once that entire channel is done and the dwarfs have dug out the pattern of one-tile paths and columns, smooth the same one-tile paths, outer walls, and columns as on the top level. After that's done, channel out the same spaces which you channeled before.
Repeat that for every z-level that you want to be open.
Once you're done, you've got a large, many-z-level open hall full of beefy columns, with fucking everything connected by precarious one-tile wide walkways, and everything is smoothed. If you built your columns 5x5 as I suggested, you can hollow them all out. Use a couple as stairways, while the rest are perfectly sized for workshops, bedrooms, and offices.
Bonus Dwarf: If you have an aquifer, tap it from below and have it fall the entire height of the fortress as a pattern of waterfalls, falling into holes on the bottom level to flow away to the edge of the map.
Extra Bonus Dwarf: Build a large hydropower system using the waterfall outflow.
Super Extra Bonus Dwarf: Pump magma up to the bottom level of the fort and into small ponds. Build your smelters and forges on little islands over these ponds.