Loft conversions - hip to gable

[Fjgb]

Hi, we're thinking of getting our loft converted. We live in a 1930s end of terrace and would have to change the roof with a hip to gable conversion and a rear dormer to fit in the stairs. We'd love to hear from anyone who has done this, and any recommendations of builders who have experience in this, because it's a little more complex than a regular conversion - in particular we are hoping to avoid losing our wonderful stairway stained glass window, but not sure if we can fit the stairs in anywhere else.

In addition, any insight into building regs and fire doors much appreciated. We're in Lewisham borough and I know there are differences to approach, but hoping again we don't have to lose our original wooden doors to replace with fire doors.

THANKS!