My tractor has, prepare to laugh, a roof of 1/2" exterior plywood covered with a clear vinyl shower curtain. A *used* vinyl shower curtain in fact. A heavy-duty one, though, does that make it sound any better?
Yes, I
can hear you laughing
It is currently sitting in the garage but survived 3 months of use last year with nary a sign of ageing or damage. I would like to think I can get at least another 6 months out of it. After that, I will either have to find another retired shower curtain <g> or switch to some sort of more sensible material. I keep hoping I'll come across a scrap of the adhesive stuff they use as ice-and-water barrier on the lower edges of roofs under the shingles.
I am not really suggesting you permanently roof your coop with shower curtains of course
but if you want time to ponder your options it might be useful. I just stretched it tight and staplegunned the edges (folded for strength) to the underside of the roof plywood.
If it were me I'd either put roofing paper over the plywood, or some thin lightweight tin (you can use recycled, BUT you will have to use or caulk all the nailholes, and depending on the construction of your roof you may have some issues with nails/screws sticking thru the plywood to menace your chickens' heads, so plan ahead to avoid that if you want to use tin).
Pat