My long-standing method is less simple than the one shown, but I thought I'd share anyway, as it has things in common with some of the 'improvements' suggested.
__^__
O_X_O
H_X_H
_ OXO _
#\_#X#_/#
####X####
# = Undug stone/earth.
_ = Surface and/or floor
\ and / = ramps
O = Built walls
H = Fortifications
(to be replaced in this instance with Windows, and maybe some provision for walls at the corners,
but in this design there's the stairwell supporting the 'roof' so corners can also be unsupporting,
noting that during construction you need a temporary floor to construct the corner)
X = Stairs
^ = You can cap with a hatch, here, although I usually have some temporary steps and scaffolding,
this gives outside access to allow complete roofing-over without leaving a worrisome opening.
######### ######### ,.,.,.,.,
######### #^^^^^^^# .VVVVVVV.
######### #^.,.,.^# ,V V, HHHHH OOOOO +++++
######### #^,###,^# .V OOO V. H+++H O+++O +++++
####X#### #^.#X#.^# ,V OXO V, H+X+H O+>+O +++++
######### #^,###,^# .V OOO V. H+++H O+++O +++++
######### #^.,.,.^# ,V V, HHHHH OOOOO +++++
######### #^^^^^^^# .VVVVVVV.
######### ######### ,.,.,.,.,
.........
.\|||||/.
.-+++++-.
.-+++++-.
.-+++++-.
.-+++++-.
.-+++++-.
./|||||\.
.........
That design comes from the wish to make a pillbox-style observation tower for archers/etc that couldn't be got at by your standard building-destroyers, and goes back at least to 40D, when channelling wouldn't automatically create up-ramps on Z-1. The other floor (or more!) of the tower could be used as bolt storage, food and drink repositary, barrackroom, or just done away with.
I've previously also made designs with ground-level "extended", but still sufficiently ditch-protected fortifications as artillery (catapult) emplacements, with stone storage on the extra floor or straight from the mine-workings at Z-2, guarding the approach-road to the main entrance. I've also extended the staircase up and out into 'skywalks' that connect the top of various towers as well, to aid rapid deployment of archers above and below. (This was also well before the current breed of flight-mounted enemies, when golden eagles were the only real flying menace most of the time.)
When planning such pillboxes/watchtowers, I'd generally dig the first into-ground stairwell, then build the above-ground stairwell, then the walls around it (careful not to seal anyone in), then dig the ditch. Then, at leisure, I could link this stairway below-ground without needing to to be outside (on the ground, at least) for all future construction efforts. (Inclusive of getting onto the roof from the side... I'd build out from the incomplete upper-floor walls, stairs up, finish the roof, then deconstruct. If I felt safe, I'd get someone out in the wilds to retrieve the deconstructed materials from the ground.)
A more modern version that I've used, on occasion, includes a wet (could have been magmaminous) moat, but also a dry one to deal with amphibious enemies who don't mind getting wet:
_ _ OXO _ _
#~~#\_#X#_/#~~#
#######X#######
I don't actually believe that helps, much, but I find it aesthetically pleasing.