ᐅ Creating an Attic with a Single-Pitched Roof

Hello forum,

we are buying an apartment with a pitched roof.
We want to use the height to create a suspended ceiling or essentially build an attic space.

To explain briefly, here is a floor plan image.

We plan to build the attic from the wall at the bottom of the plan up to the 2.37m (7 ft 9 in) long wall. The height there is about 1.50m (5 ft), enough space to store boxes.

My idea was to attach wooden beams to the walls on the right and left sides of the plan. Additionally, one beam from the middle of the wall to the bottom of the plan. Then cross beams spaced at xx cm (xx inches) intervals. Under this structure, drywall panels, then jointing and finishing, and on top OSB panels.

Now the questions:

Is this generally feasible?
How strong should the outer and the middle beams be?
How should they be fixed?
What spacing should the cross beams have?
How strong should these be?
What else should I consider?

So, should the beams run above the kitchen only, or the entire attic? If the latter, would the access be through the open space in the kitchen?

If it is the entire attic, I think a height of 1.50 meters (5 feet) is quite low – or how high would the roof space be at the start?

A 6-meter (20 feet) clear span carries a significant load, even with intermediate beams. Wouldn't it be better to have a structural engineer check this?