We used sheet metal and screws for the new coop, for the same reason, saved lots of money, some already available, etc. But I know I will have to deal with the condensation problem on the inside of the roof before winter. I have another metal coop that literally dripped water all over everything during winter when it was below freezing during the night and humid, but well above freezing during the day, not unusual around here.
I suspect the metal siding will work out much better than a metal roof (not sure what you are using for the roof.) Most of the dripping I had was from above. I am hoping that insulating the roof/ceiling will take care of it for me.
If I could figure out how to get back to p. 1 of the post and not lose this, I might sound a little smarter....