I'm just wrapping up 4 months of flowering in a DIY grow tent.
I used a "0 degree Celcius" ice fishing hut.
6x6 x 7ft inside and I've been flowering with a 940W HPS
I hung black/white poly , lining the walls and hung a 4foot diameter parabol reflector in the ceiling, attaching the ducting for my 450 CFM inline exhaust to the opening in center of parabol. intakes are 4" tubes, passive.
it's been working like a fricken hot damn and was ridiculously cheap to set up.
I didn't have to damage the ice hut at all and when I've taken everything down at the end of this weekend, the ice hut will be ready to go fishin again when winter comes LOL
lots of pics of my set up in the beginning of my grow diary.
I've been using a panda plastic 4x4x8 like yours for almost 2 years. I spent a few bucks on angle brackets for the corners. I also used square pieces of wood on two sides (opposite corners) to make it stiffer. Each piece of wood has a ducting take off collar, for attaching ducting from my hepa filters.I made a nice one with spf lumber 2"X3"X96", a 25' X10' roll of reflective black/white reflective plastic, wood staples and 3" wood screws.
It's has 48" X49" interior size with an inside height of 84". To make it bigger I can just rip the plastic off one end and add more wood to extend it.
With real wood I can hang something really heavy if I want.
https://www.icmag.com/ic/picture.php?albumid=66667&pictureid=1632153