Hey man, bit of greenhouse experience, built a kit by myself and help put a couple others together. After having done a couple, I'm pretty confident I could just but get a conduit bender and make my own. But if it's your first, I highly recommend a kit.
With twin-wall, you will need some pretty large diameter conduit (at least 2 inch diameter, probably even more.) and you'll want to make sure you sink your poles you will be using for walls below frost depth, and lock them in with cement. When you do this, make sure the top of all the conduit you are using for the walls is sunk into the ground so that their tops are all near exactly the same height as each-other (use a transit here,) or when you go to put on the roof, you'll find the peak is not straight going across, due to irregularities in side-pole height. You also really want to make sure your initial footprint is square, or everything will not go together correctly. Poly sheets don't bend, flex or stretch like poly film would, so you need to be much more accurate with your build, or you will end up with a nightmare trying to fit sheets next to each-other across a distance.
For something simpler/more forgiving of construction error, you can also take some smaller diameter conduit, still above 1 inch diameter though, and just pound them into the ground a couple feet. Take time to create a perfect footprint still, as above, but without concrete, and make sure you pound in your conduit to the same height as all the others in your wall, Put your peaks up and then run wiggle wire channel along all applicable edges so you can stretch poly film across. Run treated boards along the base of the sides to have something for the side walls to lock into, and consider roll-up sidewalls as well. With this, you don't worry so much if you fucked things up going out of plumb, because you can just stretch the plastic to fit whatever.
You also might do something super simple that allows wind to whip through, like the shade cloth guy above, but this is, (I assume,) just overhead, with no sidewalls, and the overhead is only filtering light, so will allow water to drip right onto your plants during rain events. Just depends on what you are looking for though.
At the very least, if you are looking for overall weather protection, and have little construction experience/tools, go with a stretch poly kit imo.
