This image is unfortunately an horrendous example of roof cleaning done badly. The seal haas been put on the roof whilst wet and Locked the tiles into looking like this. Please believe us when we say cheapest isn't very often best. Your roof needs to be treated with care if you want it to last. Arranging things like pressure washing, or sealing by people who have no training is not the way to do this.
Get a team with experience in roof cleaning. How many roofs have they cleaned? Can they show you local examples? Do they have customers who would be happy to provide a reference of work? What are their reviews like?
Basic questions and research to complete.
Should i clean my roof?
Roof cleaners near me
Roof cleaners lancashire
Roof cleaners burscough