Metal is the "go to" material for shed roofs and side, and for good reason. Compared to most other options, it is low cost, easy to install and easy to maintain. For housing poultry, however, it has it share of problems. Hot in the summer, cold in the winter and it traps moisture within, making it really cold in the winter.
First.......Google "condensation in metal sheds".......this may give you some insight into the problem.
Compounding the problem are the birds themselves, which create lots of moisture and unless it escapes / is removed, will create a lot of health problems inside the shed. The moisture tends to condense on the inside when you least want it and can rain down on the birds, creating cold damp conditions for them and that leads to all kinds of health problems. A dry bird is a warm bird.......no insulation needed..........insulation in a metal shed is needed to prevent condensation, not to keep the warm air in........as you say........that can't happen since it is so open.
So open is also good for ventilation.....fresh air and removal of all that moisture........unless it is so open that it becomes drafty.........think wind chill. That matters most in the winter. So the trick is "well ventilated with no drafts", which almost seems like an oxymoron. How is that possible?
So while it may seem like birds can and are raised in just about any old type of shelter, one that gets it all right and optimal for the birds health, safety and comfort is in truth a complicated piece of work. Books have been written about it.
Not saying it can't be done, nor that it shouldn't be, but you will need to do some homework to deal with the issues of successfully raising birds inside a metal clad shed.