I find that all the conservatory roof/guttering type work is all year long. I get a lot more guttering than cons. though to be fair. I always try and keep a bit of this type of work to turn to when its raining. If I have plenty on I won't chase it, if I don't I will mention it to my customers. Tend to be chasing it more in the winter, due to the weather.
Try to make it a yearly thing. Keep a note of when you did it, then you have something a bit more concrete. I charge 30-40 pounds an hour for this type of work. Don't want to take the mickey as I don't advertise for this work, its my window cleaning customers. My mate who advertises is up around 50.