The Giraffe and the Pelly and Me by Roald Dahl
When Billy joins the Ladderless Window-Cleaning Company, he gets a lot more than a new job. First he makes three new friends, then it's time to get to work cleaning all 677 windows of the Duke of Hampshire's house. The Duke is not only the most wealthy man in the country, he's also the most generous. Can he make Billy's lifelong dream come true?