8mm or better. 6mm breaks down too fast. Also the slots these panels fit into is about 12mm so hey ask for the proper thicknesses. Also when putting them together , silicon and roofing self tappers.
Boilers are better to provide radiant heat throughout from a humidity perspective, plus all the CO2 released can be captured, plumbed and released into the greenhouse
The automated blackout systems are " built to suit" once the structure and equipment is in place
Building the jig is the hardest part IMO. It took me forever to grasp how to get the layout done. His video and plans have a few things that are missing though but overall they are decent. I would recommend painting the struts to protect them though (at least on the part that is touching the plastic). Let me know if you need some help or info. IN the video it makes it seem like he is using 2x2s but in fact they are 1x1s that are glued together to bend easier. I bought the plans from this guy (shamrock Aquaponics) but decided to change it up a bit. Mine is 18' across instead of 16' like his plans (although he is showing a larger size in the video cause I think he sells 3 plan sizes.)I added about a foot to the height. Wind rating is 150mph and the gothic arch design is the best for snow load seeing how I am in Maine that was a necessity. If you know what you are doing though, I think the plans are a little unnecessary. I would also highly recommend digging a trench on both sides and laying down prefabricated wick drains to prevent the water from pooling and then cover with gravel. You also may want to check out his passive solar design if heat is a big issue in your area. End wall fans work okay but not so much when its mid summer.