Would you like to GET PAID to write a book?
If you're thinking this is plain fantasy, think again. All professional writers get paid to write their books.
How? They sell their books via proposals before they write the books.
A book proposal is a document which convinces a publisher to buy your book before you've written it. Your proposal says, in effect: "Hey, I've got a great idea for a book which lots of people will want to buy. Do you want to publish it?"
Think of it as a combination brochure and outline of your proposed book.