Grow space- I built an 4ft x 4ft x 7ft enclosure in my garage.It is constructed of 2x2 firring strips , coverd with 4 mil black visqueen with insulation inbetween.
Walls are covered with mylar . I used from home depot they have a version of heatshielding(aka the reflective stuff with the air bubbles)much cheaper than products geared toward horticulture but much cheaper. I used this in the ceiling to help with heat from light and to block IR.
This whole system was cheaper than a tent