There are 3 types of loft renovations.
The most popular is the Dormer, this is where there is an extension on the roof which projects vertically on the sloping roof.
Hip to gable extends your property on the sloping side, effectively replacing the sloping roof with a vertical wall (the gable).
Mansard loft conversions can be thought of as an extension across the entire plane of your property’s roof. This type of conversion changes the sloping side of your roof to an almost vertical side.