Well before you decide on design, figure out your needs. How many birds are you going to keep? How many to start? Are you sure you may not want more later? (We all break and get MORE! hahaha)
Figure out if you want a moveable structure or something in place permanently. How much wood & supplies do you have to build, is it just enough, more then enough or will it leave you short? Do you have $$$ budget in mind for what you need to go over?
Once you establish that, you have to decide where you want to keep your coop on your property. Is it going to be in wide open space with lots of light? Could they get hot in the summer and need shade? Maybe something with a lot of roof or overhang is a good option. Especially if it rains and drainage is an issue in that location.
Then I guess from there you could do ANYTHING you'd like to do. After all that it finally gets FUN!
Just remember, ventilation or shelter from drafts is important. I forgot about that and found when we built ours the winds came mainly from the West, so we physically had to shift our coop and run so the winds stopped coming in through the vents we had at the peak of our roof. Now everyone is happy and warm this winter.
