We always price by how long the job will take
including
ease of access
type style and age of gutter
flat roof access
amount of downpipes
closeness of trees overhang bushes
there are many ways for the job to take much longer than expected and as usual experience is the key
to get experience you need to do the work, don't charge too high while learning but once you understand the in's and the out's charge accordingly
to be honest once you know what you are doing you tend to charge high to recover the losses you made while learning
It is hard work but good work and can be done in all weather, try to schedule the work losely so you can keep it for a rainy day when you can't clean windows
Good luck
Gordon