Dahl certainly uses formula for his writing. His books comprises of some extremely bad people and some extremely good people. Here's his own words:
I have to disagree with him here. Is it absolutely necessary to have the old classic good people v/s nice people scenario every time? No, I think.All good books have to have a mixture of extremely nasty people - which are always fun - and some nice people. In every book or story there has to be somebody you can loathe. The fouler and more filthy a person is, the more fun it is to watch him getting scrunched.
It has been mentioned that he rewrote his books many times - until he was sure that every word was just right. The original draft of Chocolate Factory is titled Charlie's Chocolate Boy, and has a far different plot from the existing version it seems!
Also, his books were of their period. Featuring horrid teachers and such, eg., Miss Trunchbull in Matilda and Captain Lancester in Danny the Champion of the World.
Last but not the least: his school reports. The below is taken from a page in his books, entitled "Roald Dahl's School Reports". I had some laughter reading this:
SUMMER TERM, 1930 (aged 14). English Composition.
"I have never met a boy who so persistently writes the exact opposite of what he means. He seems incapable of marshalling his thoughts on paper."
EASTER TERM, 1931 (aged 15). English Composition.
"A persistent muddler. Vocabulary negligible, sentences malconstructed. He reminds me of a camel."
SUMMER TERM, 1932 (aged 16). English Composition.
"This boy is an indolent and illiterate member of the class."
AUTUMN TERM, 1932 (aged 17). English Composition.
"Consistently idle. Ideas limited."