9.75 M is absolutely huge for a ridge height of a two storey dwelling....
if you dont mind me saying so its bordering on the ridiculous....
lets assume the ground floor level is 150mm above path level.... then lets assume a healthy 2.6 ground floor height, 250mm floor thickness, 2.5 first floor height and 250 ceiling thickness, this leaves you with 2250 to the top of the ridge....
realistically this doesnt leave you with habitable space that conforms to the regulations for a habitable room, however you can use it for non-habitable uses....
and also remember that if you install a fixed stairs serving your attic it then becomes a third storey you ned planning permission for the attic conversion.