drain slope means raising toilet, for Midden1
Bob (Midden1) said the toilet drain required a slope (normal) and this forced the toilet to sit higher than the existing floor.
Bob, have you read other threads about sealing around the toilet base? People always talk about leaving a space at the back of the base so you can notice if and when a leak happens. If I had your situation, I would build up a base using ANY material at all that matched the design and esthetics of the space and the other occupants' desires. Any material. You don't need to be told here what the right material is, as there is none "per se".
You have several ways to choose from, to build up, using different methods. Pillars, flat layering, single-piece (monolith), etc. What might be useful to discuss here is whether to "liquid layer" (i.e. glue, cement, caulk, grout, whatever) underneath and above the material to ensure it touches the floor continuously, with no voids underneath, or to use the pillar method, a practice used in stone-laying. You can layer flat material, in separate pieces, or in whole piece layers.
David