To start though, a few basics and things that helped me:
*Go as big as your space and finances will allow, the more space your chickens have the happier they'll be. This also allows for chicken math, if you decide you want more chickens later you'll have some extra space.
*Lots and lots of ventilation. As long as you there are no draughts, humidity and overheating are far more dangerous than cold.
*Build in a way that makes cleaning as easy as possible. For me that meant a coop raised to a comfortable height with one side that folds down. It's also not too deep so I can reach the whole coop from the open side.
*Look into large spill proof feeders and waterers so that you don't have to constantly refill and change food and water. There are many designs on here so you can find one that fits your needs.