The untreated plywood I used for the mews roof developed some black mold on the underside this summer. I thought it would last at least two years, but I guess with the spring rains it got wet and didn’t dry fast enough. On the suggestion of some other falconers I switched to a tin roof. It’s $25 or more a sheet new, but after posting an add on Craistlist I found some used sheets for $10 a piece. Three of the sheets were quite rusty on one side, so I spent a few hours with the angle grinder knocking the rust off. I also painted the sheets to stop further rust development.
I had to add additional roof beams to the mews as the sheets are only 2′ wide, not 4′ like the plywood was. I used two L-brackets, one per side, on each end of each 2×4 to secure the beams. The roof tin went up relatively quickly and without hassle.
I also added some vents to the high side of the walls right under the roof. Changing from wood to metal should take care of all the mold problems, but the extra ventilation can’t hurt.