I have the same type of Dormer walls in 2 of our rooms, you didn't mention if the wall is upstairs, downstairs, or if it's part of the triangular roof. Usually Dormer walls like those are usually found upstairs. You can, however, it's not cheap at all. If the slanted wall is part of your roof, then that could cost quite a lot, because it requires rebuilding/remodeling your roof as well. You didn't mention the dimension of the wall, and you left out some important details in order to answer your question. Here in the US, it's expensive.
You have this question in ( DIY ) Are you a professional carpenter or building contractor? because that's what it would require, ''if it's attached to your roof.'' You'd need to pull a building permit from your town/city here in the US.
It's nearly impossible to give a estimate without the missing details.