I converted a small playhouse years ago, and added a bump out for roosts, increasing the interior square footage and an external nesting box. I have a fully enclosed run around the coop, raccoon tested and secure. Number of chickens have ranged between three and nine, currently at 5 1/2 (bantam cochin). I'm going to feature some things I really like about the housing.

Look at that great color! Well okay, I could use the paint job. Ever wonder what to do with that "original artwork"? There's my external nesting box, two spaces.
Note to the right side of the picture that my chicken wire is held down with screws and fender washers.

Inside. Hi Peggy! It was a challenge to waterproof this. I ended up using cut up bike tire tubing.

Food is hung inside, and crushed oyster shell available in a bread pan I picked up at a garage sale and nailed to the wall. There's Clover, wondering why she only has dust in her feeder.

I added a window on the north side, it really isn't complicated to add lighting. I merely took two picture frames the same size, cut a hole, and fixed them together one on the inside one on the out. They're caulked as well. You can see a little ventilation hole up to the left, this is not the main ventilation.

This is what I use for ventilation, register covers. There's hardware cloth on the outside. They provide indirect movement of air.

I have a number of things that that they can stand under & stand on top of. A slanted bench shingled, a very large juniper branch, an old picnic table partially shingled. Here you see I sectioned off a portion of my run with plastic fence for my Java hen who hatched out our new little cochin. They have their own roosting box. I'll snip the zip ties and take down the fencing when they're ready to co-mingle.
A few other points in my setup:

I have an old patio umbrella that I use for shade. I have it held down in multiple points with zip ties. The exit doors to the run are always open, even in winter, although I will close them down in bitter storms.
I fixed a door spring to my coop door so that I could enter and exit and have the door shut behind me.
I've expanded the run three times, and this year will be another expansion. Chickens are a crazy obsession!