Rule of thumb for ventilation is it needs as a minimum 1 SF of vent space for each 10 SF of floor space. Mine is a Woods coop which sets the standard for ventilation, and even buttoned up with all windows closed, it has about double that. With all windows open, more like 3X to 4X times that. In some ways you can think of a Woods house more like a covered run with three sides enclosed. And that works in even the coldest climates. In the wide open configuration, it also works equally well in warm conditions. In my case, from extremes of 100F down to -5F or so.
It is possible to do that without drafts in a Woods house as the basic design is a rectangle in a proportion of about 1.6 depth to width, with one narrow side open to the south. Roosts are found at the far back as far from the window screens as you can get. So even when the wind is up, the air in the back is nearly dead calm. Doesn't seem possible, but that is the way it works. But flip the orientation to vents and screens on the wide side and things change regarding drafts. You still need the same amount, but you need to need to employ different types of baffles to limit drafts. Nest boxes and droppings boards beneath roosts. That type of thing.
I'm using deep or built up litter over a dirt floor and there is no smell of ammonia or other. But my birds spend most of the day outside and I'm at less than half of it's capacity, so the birds have 8 or 9 SF each, plus wide open ventilation so that would be most of the reason why.
BTW, there are three gas products that foul (fowl?) the air inside poorly vented houses. They are water vapor (moisture), ammonia and CO2. All three are emitted by the birds themselves and need to be vented to the outside. Most people do not vent enough out of the mistaken belief it will be warmer for the birds if they don't. That actually works against them. Tight, closed up houses experience a buildup of moisture (most of which comes from the birds breathing), leading to damp......meaning cold and miserable.......conditions. Dry is warm and well ventilated is dry. As for cold conditions, the birds have feathers and can stand a lot.......if you give them a chance to.