Cost of changing the pitch of the roof, as part of a loft extension?

[Quinteszilla]

We have an end of terrace with a Hip, or Pyramid roof (so high enough for a loft).

But due to the shape, it is difficult to plan the staircase, as ideally it should come in the vicinity, and above the current internal staircase, but because of the roof this is not possible.

Any dormer would also be very small.

I am thinking just skylight windows on the front, changing the shape of the roof on the side where the staircase is, and a dormer at the back.

I am thinking changing the side to a "half hip" rather than hip. Or, to gable.

Any ideas or suggestions?

It is a conservation area...