Why access changes the job
A slipped slate near the eaves of a low extension is not the same working situation as a slate beside a chimney on a three-storey terrace. Height, roof pitch, conservatories, narrow side passages and public pavements all affect access.
A quote should allow for the actual route to the defect, not assume somebody can reach it from a ladder.
Ladders have limits
Ladders are useful access equipment but they are not a universal working platform. Roof ladders, towers, scaffolds and other systems may be needed depending on the task.
If a contractor proposes scaffold, ask whether it is included in the stated price and how long it is expected to remain.
Shared and terraced roofs
Terraced properties can involve access close to neighbouring roofs, gutters or chimney stacks. The repair boundary is not always visually obvious at ridge level.
Make sure photographs show where work starts and finishes, especially if adjoining coverings look similar.
Use the access while it is there
When scaffold is already in place for a chimney or valley repair, it can be sensible to inspect nearby high-level details that are otherwise difficult to see. That does not mean inventing extra work.
A few clear photographs of sound areas are just as useful as photographs of defects.