From Stephen King, Idirs Elba and Matthew McConaughey's Twitter accounts:

 

Looks like it will be starting someplace in the middle of the books, although it will start with the first line from the books.  The article says a lot of it takes place in out day, in the modern world.  Check it out below.

From EW:

After many years, and many attempts, a film version of Stephen King’s The Dark Tower is finally getting underway with Idris Elba confirmed as the gunslinger and Matthew McConaughey as the mystical foe known as the man in black.
Both the author and the movie’s director and co-writer, Nikolaj Arcel, spoke exclusively with EW about the plan to begin adapting the six-shooter-and-sorcery tale — which spans eight novels, assorted comic books and short stories, and is frequently referenced throughout King’s body of work.
“The thing is, it’s been a looong trip from the books to the film,” King says, putting it right in context: “When you think about it, I started these stories as a senior in college, sitting in a little sh-tty cabin beside the river in Maine, and finally this thing is actually in pre-production now.” He laughs. “I’m delighted, and I’m a little bit surprised.”
Arcel, who is best known for the 2012 Danish film A Royal Affair and for co-writing the Swedish version of The Girl With the Dragon Tattoo, says he will start shooting The Dark Tower in South Africa in seven weeks, and Sony Pictures plans to have it in theaters on Jan. 13, 2017.
Arcel will share screenwriting credit with Anders Thomas Jensen, Akiva Goldsman, and Jeff Pinkner. The producers will be Goldman and his Weed Road company; Ron Howard, Brian Grazer, and Erica Huggins of Imagine Entertainment; and Pinkner as executive producer.
“What Stephen King does best is mixing the everyday, or what you might call the mundane, with the fantastical,” says Arcel. “In my view, [The Dark Tower] novels are a mix between sci-fi and fantasy and modern times. That exact mix is so Stephen King.”
King says the movie will open with the first line from the first book. “It should start that way,” he says. “I’ve been pretty insistent about that.” He even tweeted it out today:
“[The movie] starts in media res, in the middle of the story instead of at the beginning, which may upset some of the fans a little bit, but they’ll get behind it, because it is the story,” King says.
Arcel declined to specify which books his movie focus on, but he did offer this clue: “A lot of it takes place in our day, in the modern world.”

For all your King news and info follow Discordia 19 on Twitter and like us on Facebook