Hi, I'm currently half way through building my Ark for my urban garden so i know exactly what your going through now.
The main things i've found as i've been talking to breeders and trawling the web are:
~ be realistic with the number of chickens you wish to keep. Large fowl or Bantams? Always make your coop too big never overstock and allow room for them in the run and coop and big enough nest boxes. The Defra website does help but the measurements are a minimum.
~ has to be Predator safe, and rodent safe, You don't want rats or mice in your coop or under it. And then the obvious fox threat! There's a reason Game keepers put a electric fence around there pheasent pens, 6ft of fence won't stop a hungry fox, also they can dig under the fence. SO you need to lock them up every night without fail as you bet the night you forget the fox will be in.
~ Draught proof. Chickens are find in cold conditions if they are not wet or in a draught but they need ventilation or you develop respiratory problems.
~Material selection - Needs to be warm in the winter and cool in summer. Don't make a massive coop for 2 bantams as they will be very cold in the winter because there body heat wont heat the huge area.
~Feeders and drinkers where your going to locate them and how much they need to hold as there are guidelines on litres per chicken.
~ cleaning. needs to be easy for you to clean on a regular basis also egg removal, make it as easy as possible at a height that suits you.
I hope this has helped.
Keith
