I built this attic in 1996. See below for the most significant design drawing.
The design gives a bare minimum headroom in the middle of the attic, with a bare minimum headroom under the middle of the attic in the two rooms below, but a very good, airy headroom elsewhere in the lower rooms. It also gives a bit of space behind the backs of the built-in seats in the attic, to make the attic a bit less claustrophobic. It works: it doesn’t feel the least bit claustrophobic, now it’s finished.