You're in the right section to be asking. I have collected lots of ideas making several coops, nest, roosting area, open area, long run, etc.
Weather is a consideration. Ventilation Hot/Cold (Chickens make heat and moisture), Each chicken = a 10w bulb. Make a 4"-8" Draft at top (can close it off depe Inding on season).
River sand is better floor for summer and cleans easily like kitty litter, but is cold in winter. Straw/Woodchips work well too. Heat lamps over water and warm area in winter. Mine is open on bottom on the ground, and I have to scrape and dig and replace dirt lol. I use straw and woodchips along the edges (seem to keep the chickens from digging out). Packed dirt along the outer edges.
You need approximately 3-4 feet per chicken.
Mine is a 8' wide x 16' long and 8' tall sloped in the back to a 4' fence to ancor to.
8x16=128
3.5x3.5=12.25
128/12.25=10.45 (between 8-14)
So about 10 chickens would be happy. I have 10 in there and seem to be happy.
Up to 4 chickens will share each nest.
I have 4 nest with different shapes and sizes. About 12"x12"x12" should be plenty, I have seen just about every shape of nest in here except for a football helmet.
I also have a 2'x3'x16' detachable run that I can use for a temporary isolation pen.
Chicken wire. I use smaller wire on the bottom (in case I have to put smaller chickens in there, don't want them to crawl thru the hole playing peek-a-boo with the predators).
Chickens like to roost, about 8" for each chicken, so about 80" for 10 chickens, I usually figure a little more.
A tractor is a good way to move the fertilizer makers around. I'm currently working on a design of a tractor.
I would just look at all the pictures in here, lots of great ideas.