These are the type of jobs if not used to them can end up being more hassle than what it's worth (not that i'm an expert, but have done a couple similar but not as big), on the flip side they can also be a good learning curve for any future similar jobs.
going off the pictures me personally would be going in at about £1200 -£1400 maybe even more . You've got to make these jobs worth your while IMO. 12mt is about 39ft so it's going to be hard work on the neck working at that height for ages so no point in earning a bit more then what can be done cleaning windows. Also some of the cladding looks like you will need to work the brush from side to side in between the gaps and can't just go up and down.
Is that 240m long or foot?
EDIT* posted before i saw reflections reply, but agree with him.