I realize that. I make a wall, and then try to make a ramo leading up so I can construct another level, but I can never construct another level above.
I don't see you say how you've got this working, below, so I'm going to suggest something you may or may not know (or have known)... And I know you've moved on to other questions now.
The following all in side-views, sometimes with the 'correct' symbol but sometimes with one 'representative' only.
Start from ground level...
___________ (ground/floor)
########### (rock)
Build a wall and a ramp to get on top of it
_
___O\______ (using an oblique to indicate the effective direction of ramp)
###########
You can't, at this point, build a useful ramp anywhere but on top of that lone bit of wall.
\ (actually directionless, there's no upper level you can build)
___O\______
###########
There's no way of building another level, at this point, so what I'd do is drop more walls in where you can.
Either
_
O\ a wall on top of a ground-level wall
__OO\______ the ground-level wall
###########
or
_
O\ You can hang a wall diagonally off of the top of the wall you have
___O\______
###########
Either way, the second ramp now lets you travel up to the second-level of flooring and continue.
Personally, I'd just build stairwells:
___<_______ up-stairs
###########
X up/down-stairs
___<_______
###########
X more up/down-stairs
X
___<_______
###########
> end with a down-stair if you want to be neat, but not necessary
X
X
___<_______
###########
___> You can build floors outwards from all these
X___
H_X (and even hang walls or, as here, fortifications off the side of them)
___<_______
###########
And here's how I often build towers (plan view)
+++++ The tops of the walls from the level below
+ +
+ X + A stairwell in the middle (as an example configuration)
+ +
+++++
+++++
+ + +
++X++ Set up at least one connection from stairwell to wall-tops (as floors, on this level)
+ + + (It may well be more than one floor needed to connect from centre to edge.)
+++++
O+++O Set to build new walls (/pillars) in the corners alone, and let that finish
+ + +
++X++
+ + +
O+++O (There's access to the corners from both adjacent wall-edges)
Or...
OO+OO Set both the corner pillar and one segment of edge wall per corner (direction doesn't matter)
+ + +
++X++
O + O
O+++O (Access to the corner from one wall-edge, the other planned wall segment blocks but not fatally so, and not totally blocked itself)
Then..
OO+OO Fill in from the corner to (not quite) the access-point)
O + O
++X++
O + O
OO+OO (Route of access should be obvious)
Finally..
OOOOO The remaining walls
O + O
O+X+O
O + O
OOOOO
Of course, if you also set floors to be put in to fill the floor-gaps (not shown, but you can imagine), then you can speed things up.
It's a Last-In-First-Out job queue (i.e. stack) so you can fine-tune it by defining what you want doing last first (that it is
possible to define, of course) and
then defining the floors/etc that would be handy to be done first, and it should all work itself out. But takes practice to know what on earth the dwarves will do for any given construction method.