Best approach to porch window replacement?

The front porch on our 1900s terraced house needs the woodwork/glazing replaced. The porch is approx 1.5x2m, half brick, single glazed, and with a pitched tiled roof. The woodwork, especially on the south face, is rotten and needs replaced. We can keep the existing door. I wonder what's the best approach? Prop up the roof and just replace the glazing sections, or tear down to the brick and rebuild? Thoughts, opinions, ideas welcomed! Thanks/