Re: "pole barn", this is the sort of structure that really works for us here. I've experimented with several 'tomato bus shelter' type structures, and they have really done the best even with a solid roof (not transparent) as long as you have them lined up at the edge to get as much sun as they can. Even a west facing structure that got no morning sun has been fine for them. Roof just a narrow 1.5 or 2 ft strip 6-7 ft above ground with open front back and sides. And that is something you can build from scrap lumber if you have any = free.
It is way easier than trying to make a plastic roof, which is costly not only the plastic itself but also more demanding of structural support to make it tight enough.
My old wood stacker which I've used for tomatoes has a little roof on it made of a few pieces of clapboard. Works fine for a tomato!