I had the Harry Potter Film Wizardry book as a Christmas gift, which is amazing - and heartily recommended to any HP fan.
Some of the info contained within people may already know anyway, but if you will allow me to reveal some snippets for discussion here, I will post the odd fact.
To start, I had wondered about the change in the appearance of Privet Drive. In film 1 Chris Columbus found a street in which to film the outside scenes, and the residents of the street all gave permission for filming, but when production ran over the initial schedule, the neighbourhood requested too much money to make the location available again for Chamber of Secrets. Therefore, Privet Drive was BUILT on studio grounds at Leavesden Studios. This studio version was then used on all subsequent films with the exception of film 3 when to accommodate the shot of Harry walking away from the Dursley's, they had to film at a practical location just across the road from the studios that had been built from scratch while films 1 & 2 were being made.
The cupboard under the stairs was the film series' smallest set, and the 4 walls were all removable to allow access for filming. harry was 'given' a small section of one of the cupboard shelves for his personal treasures.
The No 4 set designer bought most of the Dursley's often tasteless furniture in Watford.
The letters of an offer of a place at Hogwarts for Harry had to be printed on a variety of papers. Some had to be light enough for real owls to carry, and 10,000 that had to be light enough to be blown around had to be printed on banknote paper.
- Bet the residents of the real original Privet Drive regretted pushing for too much in the end!