Create attic with a shed roof

Hello forum,

we are buying an apartment with a mono-pitched roof.
We want to use the height there to essentially lower the ceiling or create an attic.

For explanation, here is a quick picture of the floor plan.

We want to make the attic from the lower wall on the plan to the 2.37 m long wall. The height there is about 1.50 m, enough to store boxes.

Now I thought we could fix a wooden beam on the wall on the right and left sides of the plan. Additionally, one beam from the middle wall to the lower side of the plan. Then cross beams spaced xx cm apart. Under the construction, plasterboard sheets, fill and sand, etc. And OSB boards on top.

Now the questions:

Is this basically possible?
How strong do the outer and inner beams need to be?
How should they be fixed?
At what distance should the cross beams be?
How strong should they be?
What else must I consider?

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

If the entire space, I find 1.50 height already quite low – or how high would the attic space be at the beginning?

A span of 6m without support is definitely quite a load (even with intermediate beams); shouldn't an engineer take a look at this?