A couple months ago I finished painting the roof of the barn, but hadn't gotten around to posting it until now.
Below are the paints and pigment I used. Using a sponge brush, I applied the various rust colors including Burnt Umber, Brown Iron Oxide, and Burnt Sienna to the tin and tried to leave some un-aged areas in similar spots to where they are on the actual barn. As a bit of an experiment, I mixed in a bit of Earth Pigments Orange Iron Oxide to add a little texture and help blend the colors together. I highly recommend these pigments by the way. They are reasonably priced and can add a lot to a model. I've just barely started to learn to use them, but see they have great potential.
Here is one side of the barn. It still has a little shine to it which I'll mute with some flat clear coat after I get all the wood painted. Waiting until then will avoid over-spray which would seal up parts of the wood resulting in inconsistent paint absorption.
Here are a couple more shots from different angles. Depending on how the light hits it, the colors look quite a bit different. Once everything is finished, I'll take some photos in better lighting.
Just as a point of reference, here is a shot of the roof from the Walking Dead Season 2, Disc 2 BluRay. Once I get around to painting the wood, it should bear some resemblance to what is on film.