I used Lowe's dirt cheap "Barn Paint" on my barn, my coop, and a wooden shed. Its like $90 for a 5 gal bucket.
First coat applied as what I can only describe as a rather feminine shade of pink on my barn and coop, both made from hardieboard. Second coat went on a proper red. One (the barn) was sprayed on, the other was rolled on, with a trim brush to cut in. Results the same, both cases. Its holding up nicely to the FL sun and the humidity.
Three coats went on the shed, made with outdoor/exposure rated wood panels, 3/8" thick. Four coats in places. Mildew appearing everywhere except the S facing wall. Paint adhesion is good, but apparently offers no protection to the wood underneath. In addition to the mildew appearing on the surface, there is the usual warping associated with dry/wet cycles in wood as well. VERY displeased.