I made this coop and seem to remember there was an error in the measurements for the door. I sent corrected measurements for the book but I can't find that email. I adjusted the measurements using the door width as the "starting point". Hope this helps.
ETA - Just found my comments that I sent in:
I bought the Chicken Coops for Dummies book and have started making the Walk in Coop. The measurements for the front wall framing (pg 254) are not correct. Either the door header pieces should only be 34" or the measurement to the right jack stud should be 44 1/4". To keep with the other measurements for the studs, I would suggest shortening the door header to 34". I would also suggest giving the measurements for the left studs for the right and left walls if possible. It would make building the frames for those walls a little easier since you would know where to start putting the studs. I want to say that I have really enjoyed the book and it has given me the courage to go out and do this by myself, I was just a little disappointed that the measurements were off on the front wall and it didn't occur to me until after I started framing it out. I was able to adjust the frame to make it work but I thought that I had messed up when assembling the wall.
Hope this helps