A pergola that becomes a sukkah every year
A rabbi asked for something his whole congregation could sit under. So we built a permanent pergola: it stands in the garden all year, and come Tishrei the s’chach goes straight across the rafters and it is a sukkah.
Posts on raised steel bases, beams bolted through, rafters lapped over the top. Built once, and it goes up in an afternoon every year after.