Raise the roof structure

The following, I live with my partner in my parents' house on the top floor (under the roof). It used to be our children's rooms, but now we have converted the rooms into an apartment as a temporary solution. Actually, it was supposed to be only a temporary solution due to space. But now we are considering staying since living spaces in our area are scarce and expensive. However, we need more space. Therefore, the idea was to raise the roof higher and reallocate the rooms, additionally a separate entrance and a balcony are to be added. Currently, the knee walls are only about 1 meter high. These would of course need to be raised considerably. Do you think this is possible, including relocating the interior walls? And what kind of costs should one expect? We can do a lot of the interior work ourselves, such as installing the flooring, etc. Do you think 200,000 [euro/dollars] would be enough? Since I really have no idea about this, I hope for your help.

Yes, there is the first question of whether it is approvable. You find out at the building authority. The second, whether it is statically feasible, you find out from the structural engineer.

It’s just a general feeling I have. That you need the approvals is clear to me :)

But that is the most fundamental thing, if the authority says there are not 2 full stories there, then you don't have to worry any further.