Well - here's my ideas.
If going to use GH as a coop:
1- keep at least part of the roof as those panels for light AND the window vents for venting. Even in the dark, w/ moonlight, it makes it so much easier to see if you have to do chores at night or early in the AM. Any bit of light is helpful on a cloudy day - summer or winter.
2 - build a wood frame with HC over it, to cover your drain. You never know when you might need the drain. Make it tall enough that it can't be filled with debris kicked into it.
3 - Even during the winter you will need more venting than what I'm seeing in your photos. That would be both up higher and down lower. Most breeds of chickens can survive bitter cold if protected from wet weather and wind. Frost bite occurs when it's too humid in the coop and there isn't enough venting to vent the humidity out.
4 - keep the electric & water pipe(s). You could add a frost free hydrant at one end or the other - to water the birds inside. Or did you already have that option in the GH?
5 - it is my understanding that DLM will work on a non-dirt floor. You just need to add yard or garden dirt, preferably with some worms, bug-life already established (from a compost pile that has worms/bugs would be good too). I've done DLM on dirt, so don't know how it works exactly... Even w/o the bug-life, you should be able to add straw, hay, leaves, shavings, saw dust, leaves, pine needles, branches, limbs, shredded paper, shredded cardboard, veggies, fruit, popcorn and other food left overs to the ground you have and the chickens will still work it and turn it into compost. It should develop the proper molds that will break everything down - even w/o the dirt. To keep it moist enough, you could empty your waterers in it as needed.
6 - you can put roosts and nest boxes somewhere w/i the GH that is out of your way. You don't absolutely need to do a "house"(coop) inside of the GH. You could make one or two sides solid wood if wanted/needed.
A different coop:
If you keep the GH as is & aren't sure what you want in a coop, you can do an inexpensive one from hooped cattle panels. There are several plans/ideas on that with many of our members here on BYC. You can go relatively inexpensive or you can build it quite pricey! Or you can use pallets - again many ideas on BYC as well as google!
1 - an 8x8 (2 - 16' cattle panels on a 2x4 or 2x6 base) should hold 16 chickens @ 4' of space IF you have open run space, too. IF that 8x8 area is also the run, then it will hold only 6.4 (6) chickens... Since it has open area above & they free range (some, not all the time anymore like we used to), I've got some extras in two of our hooped coops (3bantams hens, 1 bantam rooster & 4 LF hens in Coop 1; 1 LF rooster & 8 LF hens in barn coop, i think; Coop 2 has 1 bantam roo & 4 LF hens).
2 - you wouldn't have to completely enclose it or raise it off the ground. There are many hooped coops doing just fine in heavy winter weather - no freezing birds. You can block wind with tarps or plastic (for light during the winter) - as long as you account for enough venting. Some have used combinations of actual vents put in, adding in windows. Some have used hay/straw bales along the bottom - on the outside to hold down the plastic or tarp or inside so can also be used for the birds to perch/jump on.
3 - if you like the hooped coop, you can later add different products to roof it instead of plastic or tarp.
4 - our waterers & some feeders hang w/ snaps so can be moved when necessary. The roosts hang as well - two of them swing.
5 - Nest boxes can be attached or freestanding. Lots of different arrangements.
Runs - from either the GH or a new coop - can be in soooo many different styles, materials and configurations. They can be moveable/portable so that you can move them around. You can make them permanent. They can be in "chunnels" - a chicken tunnel made out of wire that is about 2' tall and 2' wide - that could go in different directions, too, or be moveable to get to other areas of your property.
But then again I get why you want o keep as a green house.
