An alternative to a hip dormer conversion, a hip-to-gable is where the existing roof is extended to meet the gable end and the gable wall is then built up to meet the new roofline.
The new gable is usually built up in brick, or rendered, to match the existing gable wall.
This type of conversion can provide a lot more useable space and Velux roof-lights are installed to provide natural light and ventilation.