It's in two rooms, one of which has a higher floor than the other. We were looking to screed the lower floor, bringing the two level, but a bit of laser-level investigation has revealed that the lower floor... slopes.
The highest point is about 2mm over the height of the other floor. The lowest point is about 100mm lower. This room's about 3m x 5m, the other room about 4m x 5m.
I'm told that a screed isn't going to work terribly well - it'd just be too damn thin at one end, and would break up in no time. Putting some kind of a "dam" in place and screeding everything over ~25mm depth would leave about a third of the floor untouched.
There's a (let's call it semi-structural) dividing wall between the two, with two doorways through it. One of them has a ~50mm step, the other a ~80mm badly-done and fairly steep ramp, which will probably be getting cut off. The floor paint on the upper floor is peeling badly, mostly just the top layer, but several bits have worn through to bare concrete. The original plan was to leave the floor as painted concrete, because there's a reasonable chance of spills etc.
What would the assembled masses do? There isn't enough depth below door sills to screed the ENTIRE floor, both rooms, to 25mm+.