I have had two greenhouses. I ordered one via the internet from Charley’s Greenhouses. The latest one was a kit from Costco.
Actually both were kits that came with all the parts and some oblique directions and a list of suggested tools.
Each Kit took about three days to build.
The one I am presently using is equipped with lights, electricity, reverse osmosis water filtration system and a misting system set on a timer. It also has a thermometer that when the inside air temp gets above a set number I will get a text message that the greenhouse is too hot.