My first suggestion is not to worry too much about the cold. There are flyers in northern Canada that have very open lofts and do just fine. The birds will handle the cold as long as they are healthy.I am starting to draw up a plan to build a new loft soon. I know I will not be able to make everybody happy but it will work for me.
Okay so first off I was going to build something like the redrose starter loft, but make a few of my own adjustments.
I was planning on making it 8' long and 5' wide.
On the 8' back wall is gong to be all perches.
On the 5' wall in front of you as you walk in there will be some nest boxes.
The other 5' wall will have the door entering the loft.
And the front of the loft I was going to make some drop traps that I can close up to keep the birds in the loft, and when they are open it would be to let them out into the aviary.
No I am not going to have different sections for old birds, Yb's, hens, cocks. Not enough room for all of that, so they will just have to share what they have.
I live in Utah, so we can get real cold in the winter and real hot in the summer.
What should I do for ventilation, top and bottom? I will also like to make a door for sweeping out poop.
I was planning on making the aviary the length of the loft, with a trap above it for birds that don't come back into the aviary when I let them loft fly or on tosses.
Windows, do I need one? Not sure where I would put it if I did have one.
Flooring, what do some of you recommend. I was going to put down some sticky tiles over the plywood floor to make it easier for cleaning.
I plan on having about 15 to 20 birds in there (homers)
Thanks for any input.
Ventilation is something I spent many many hours thinking about. I ended up using grated vents in the floor along the front of my loft. they are one foot by four feet and I have eight of them (my loft is much bigger than what you have planned, you wouldn't need that many). That is for incoming air. To vent the stale warm air I have the space between the rafters in the roof screened off all the way around. I have noticed no stale smell in the loft regardless of temperature. Here in Georgia it can get into the triple digits in the summer and down well below freezing in the winter. I am very happy with this aspect of my design.
As for the floors, I used Luuan over plywood. It is fairly cheap ($9 per sheet), is water resistent and very easy to scrape. I would never use anything else.
Hope this helps some.