Anthology
I’ve seen these type of challenges before where someone suggests of creating a book where all participants contribute a chapter to the book. I'll be honest I usually don't enter in those challenges. It's a neat idea, however, there is one issue: not everyone is on the same page (no pun intended). The problem I find is that everyone has there own idea of how the story should go. Sure, you can communicate with one another but not everyone is going to have the same idea of how to tell a full story. One person is probably going to want to focus on character development while another is probably going to focus on worldbuilding.
Picture this, let's say that a character is introduced and this character as a great backstory that a writer really wanted to explore later on in the story. However, in the next chapter, the chapter that another writer is working on, that character is suddenly killed in way for another character. Again, I'm sure the different writers can communicate with one another about this, however, but this scenario shows that each writer has a different idea of how a story should be told.
Another concern I have is conflicting writing styles. If each writer was going to write one chapter each, that writer is going to write in their own style. A writing style is much like a fingerprint. It's only unique to the individual. If one chapter is written by one person and the second chapter is written by another, any reader will pick up on that. Sometimes that may throw them off, which is something a writer wants to avoid. Again, sometimes different writers working on a project together can work. Look at Good Omens, a novel by two of the best fantasy writers Terry Pratchett and Neil Gaiman. While it is a good read, you tell which section of the story was written by which writer based on the style, if you're family with their works.
So I have a different suggestion on creating a book. How about making it an anthology, a collection of different stories. There's a ton of free range with anthologies. An anthology can have an number of stories all centering around a single theme or genre. Personally, I like anthologies. I like having to read a bunch of different short stories from different writers, that way I can search for those writers and check out more of their work, if they have any more. Many great writers started off writing short stories for different anthology series such as Weird Tales. Writers like H.P. Lovercraft or Robert E. Howard or Arthur Conan Doyle. That's where I stand. Of course, this is just my personal preference and my thoughts on how we could all contribute in writing a book. Give it some thought and let me know.