Study what style you like. Study your budget. Recycled boards and such are nice, but stuff from the lumber yard is a lot easier to work with.
Consider designs/ features that make it easy on your back for cleaning, and egg retrieval. Spacious enough for the #birds you are thinking --4 sq feet per bird. The Run should be 10 square feet per bird.
Considerations also for Roosts giving space to avoid picking, ventilation, manure removal, Feed and Water set ups.
Personally I put in about 2-3 months on BYC's coop pages often up burning the midnight oil. Studying how to frame a coop. At the build I got a bit overwhelmed so then broke it down to 3 parts.
Foundation, Floor joists, floor covering:
Then 2 x 4 construction framing.
Nest Box access area (that was a day in itself)
Siding the framework.
Windows and Door
Figuring out Pitch and Run for the roof.
Trimming soffits and fascia
Then the bells and whistles: Hardware cloth and screen on the windows, pulley and ropes for the pop door. Roost building. Flower hangers and plant boxes under the windows.
It's all amazing fun.
Edited to add that I lost 16 lbs. also. Lol.
