kWelcome to BYC!
I did feed trough wall mounted on shelf so as to be 8" above floor at it's top. It is made of pvc house guttering. I did guillotine-style pop doors , cables and pulleys overhead for operating. No water in coop once they are allowed out of it. (some do confinement to imprint on chooks that coop is their home) That way in AM when you open it they all come out for a drink which means you can then close it again and do feeding, cleanup chores without chooks being underfoot. Works for me.
Lots of ventilation up high. If you have a roof with soffit or overhang even unfinished, make it where it is a continuous vent. Do gable vents if you have gables. I did a turbine vent in top center of my 8 x 16 coop. Do windows on two or three walls that open for extra ventilation in summertime.
Run power and water line to site. Install linoleum over floor if a wooden floor, then do deep litter method. Do poop planks covered with linoleum, and clean daily. Litter will last up to a year that way. Unless a tiny flock, make coop and run big enough to walk into upright. Put roosts higher than nests, and opposite each other if possible. If a small coop, do bumpouts for nest boxes and consider roof overhang for protection of access door and area from rain/leaks. Provides more roominess and that means less fighting among flock members.
Think of ALL possibilities for predators of all kinds and do not under estimate them. Chose site that does not flood, ever. If a small coop think of a drawer to pull out for cleaning area under roosts daily because that is where the poop buildup is.
Look at lots and lots of designs and do ask questions on this forum. If in urban area, test the waters with neighbors who might be affected. Check zoning too. Think twice about roosters because they are noisy.