For what it's worth:
I had been thinking about this same thing, starting about a year ago--without any idea of how it would fly. I emailed a friend who's been editing well known magzines for the past 20 years, and also author of three YA books.
This is a piece of our communication:
Me: "Hi Nina, In a nutshell: This past week I started writing pieces of from 1000 to 2000 words on my particular slant on growing up in downtown Brooklyn. I've been putting it off for along time because I anticipated it as too much of a tragicomedy, but once I started writing it, the paragraphs flowed. It hit me that I could put together a book--a first draft--within six months or so. So far I have 3 pieces, some 5,000 words. My plan is to submit single pieces to magazines, (always maintaining the copyright) and hopefully have a a goodly number of acceptances from decent magazines before I put together a book proposal a few months down the road. "
Nina: "...in putting together a book proposal you'll need the following:1) some sample chapters. yes, it would be great to have them published as articles, but beware: book publishers do NOT like to publish a book that reads like a string of magazine articles. the book itself (a memoir, i presume) needs to have an arc, a flow, a beginning middle end for it to be attractive to agents/publishers.... "