There are some authors who just know how to capture their audience's attention. In Andy Griffiths's case, he knows his readers (and potential readers) well and can hold their attention for over 45 minutes. When those readers happen to be no more than 10 years old, that is quite the feat!
His parents were SOOO terrible (they were normal) that he ran away at 8 and never saw them again! He met Terry Denton (the illustrator) because he got his food hiding under restaurant tables stealing food. Terry was wearing inflatable underpants because his parents were very safety-conscious. They met in a river after Andy ran away from the angry chef to a stream where there was a pirate ship. They made a tree house with the scraps from the pirate ship!
Terry coincidentally drew a 13 story treehouse when Andy asked him to include a bowling alley and a shark tank. Warning: There's NO peeing in the shark tank!
Fun fact: he has a Dr. Seuss tattoo from One Fish ...
He bet Terry he couldn't draw a 39 story treehouse (after the 26 story one). Terry bet he could. Andy bet he couldn't. They went back and forth for 3 weeks! And then Terry drew it, proving Andy wrong. And then Andy had to write a book about a 39 story treehouse! Baby dinosaur petting zoo --> Terry made a time machine from a trash can and brought some baby dinos back. It's kinda complicated.
It takes a year to write a book because they fly around on jet-propelled swivel chairs shooting staple guns. That's 364 days and then they write the book in a day. That's his favorite level in this book. But that one day can now be spent flying around because Terry invented a Once Upon a Time Machine that will write the book for you!
Every story needs a good looking, brilliant hero. "Are you talking about Terry?" asked a student. "No! I'm talking about me. I don't think you understand what I'm talking about."
In the next book, there's going to be a birthday room that everytime you go in, it's your birthday (party). But there's also an unbirthday room. Mainly for adults so they lose years/get younger. Terry goes in and turns into a baby. Andy has to change his diaper so he doesn't like that room.
When things go wrong, that's when the story starts. If you're going to write a story about a baby, you want to write a story about a bad baby who does dangerous things.
His book ideas come from trying to surprise his readers (the unpredictable). In the baby example, the baby narrowly escapes getting hit by various vehicles crossing the road, and then it gets hit by a little old lady in a motorized wheelchair!
His favorite book is probably The 39-Story Treehouse book because it's the biggest and stupidest! But that may change come August when The 52-Story Treehouse comes out! (The 65-Storey Treehouse -- yes, with an "e" in Storey -- comes out in August in Australia.)