Chickens and ducks require different care, and have different instinctive drives and needs. I'd suggest building the "coop" specifically for the chickens.
Chickens instinctively will go into a (secure) coop, and seek out the highest perching spot available to roost (sleep). In addition, the coop needs to have a nesting area for the hens, which needs to be at a lower elevation than the above mentioned roosting area.
Take some time to look through several posts in this section about people building coops and runs for their chickens. There's a wealth of information here.
Also, in general, a coop needs to have at least 4 square FT. of space per hen, and the Run in general approximately 10 square FT per hen.