I'm a vegetable farmer in the midwest, and grow in a greenhouse year round.
Join the "high tunnels" email list to find out more about what folks grow in them.
As for building your own & moving it around, Johnny's seeds & a few other seed companies sell pipe benders that allow you to bend the galvanized electrical conduit or chain link fence pipe into hoops for making your own. You'll also need some type of ground posts (the type you need depends on the type of soil), a bit of lumber for end walls & baseboards, something to anchor it to the ground, plastic, and a system to hold the plastic on. Many places sell UV-treated greenhouse plastic, which lasts 4 years minimum (and actually can last far longer, it just lets less light through as it ages.)
These type of structures are absolutely moveable, although it's a fair amount of work to move them depending on the size. Like a number of other growers in our area, we have purchased them used, taken them down from another farm, and moved them to our farm. If you hang around on craigslist a lot you might occasionally see a used one come up for sale, that's how I found ours. Building your own is doable as well, if you have the aforementioned pipe bender and some construction skill.
For ventilation, it can be as simple as rolling up the sides manually to 3' high or so on a sunny day.
If you are in clay or other heavy soil, anchoring the whole thing to the ground is not a huge deal. If you are in pure sand, you might have to consider concrete. If you have a only few inches of soil on top of bedrock, then anchoring a greenhouse is a different matter entirely...
Feel free to PM me for more info if you want.