I could say it, but
@3KillerBs says it better (can't wait till they finish their article). Good advice above.
Needs more ventilation, very attractive, but will be tight for the number of birds, and they WILL destroy every green thing you plant in that space.
Also, grass is a monoculture. Monocultures make for dietary imbalance. If you plan for your birds to free range as a dietary suppliment, think "polyculture" - you want a mix of legumes (like clover), grasses/grains, seeds (subnflower is popular and atractive), and herbs/forbs/flowers/veg - marigolds, fenugreek, cilantro, rosemary (chances are, your birds won't eat this - but some do), carrots, radishes, etc... Melons and squash of all sorts are popular in summer.