Design YOUR coop however you wish. As long as certain elements are present znd it functions for you it is correct. Let your imagination run!
Now getting started by identifying those key elements:
1. Size: coops should have 4sf/bird min of floor space as a general rule. This can be cheated a little with smaller breeds and free range birds that spend little time in the coop or in climates with little snow.
2. Materials- you can save a lot of money by salvaging materials like pallet wood, shipping crates, or cull wood at local hardware stores. There will be some sweat equity spent though to take these items apart. Also cull wood is sold 75% off usually but is bowed, cracked or twisted. Cracks can be cut out, bows straightened, but twists are a huge pain in the butt to make usable and those i would avoid.
Any wood that touches the ground must be pressure treated and labeled for "ground contact" or "underground" and any supports to be buried must be labeledfor use "underground." Avoid landscape timbers. They tend to warp and twist are not treated with the same chemicals and will rot after only a few years of ground contact.
Any wood not subject to the elements (interior) can be regular kiln dried lumber.
Tin or shingled roofs work fine but will get hot in direct summer sun. Providing some afternoon shade with trees will help greatly.
Insulation and heating is not necessary unless you live in extreme cold.
Coarse thread wood screws or common nails (10d min, 16d better for framing, 8d for attaching plywood) are fine for interior construction. Any fastener going into pressure treated lumber will need to be galvanized or polymer coated exterior grade to be protected from the elements and the chemicals in the wood.
3. Ventilation - coops need ample ventilation to prevent moisture build up and fresh air. Windows in walls are a staple and oversized roof soffits are great. Consider adding a roof vent if your in a hot humid climate.
4. Predator protection- all conceivable access points must be protected. DO NOT USE poultry wire fencing. It keeps chickens in but nothing out. Use welded wire or hardware mesh depending on what predators are in your area. Latch and lock all doors.
Consider elevating your coop to reduce accessibility by diggers. If the coop is at ground level it will need a solid floor, predator apron (buried fencing) or both.
5. Style- again this is your choice. Walk-ins save your back by making easy access to everything but you enter the coop daily.
Exterior nesting boxes (what i have) provide access to feed, water, and eggs without ever stepping foot inside.
6. Interiors - nesting boxes (min 1for every 2-3 birds), roosting rods (1lf of roosting space per bird), poop boards (poop deflector/collectors under roosts)(optional), feed stations (optional), water (optional). Although i list feed and water as optional plan for areas to have them even if not on a daily basis. This way if they need to be cooped up, choose to stay in during bad weather, or you go on vacation, whatever, they can have it wiyh no trouble.
How to build it will be based upon the design and how you choose to bring all these elements together. Draw it out first, think things through, be prepared to improvise during the build, and have FUN with it!
but every time I get my father to build me one! He never does it right and it’s never safe from predators 
and I just ordered a coop off of amazon and it is so tiny and the material is so cheap I didn’t expect it to be so flimsy! So I’m going to build my own! But! I need some tips on build and a design can you show me your home made coops and tell me how you built them 
