Artjak I know exactly how you feel as regards instructions I spent 3 days building 1 that was supposed to be done in a couple of hours.
After a small amount of blood and cryptic instructions that somehow had got the diagrams mislabeled and misplaced. in the end although it was fairly functional once it was assembled, it just got used for a little potting up and plant rescue.
It was to be a display model,( I used to live in a gardencentre) but with the horrid build instructions we never stocked it.
The window also got bent in the wind, it was mostly extruded aluminium and fairly light weight plastic glazing. We used to get a lot of enquiries about it, but we said it wasn't worth buying.
What ever greenhouse you do go for, try and find customer reviews. Greenhouses can be right ..@~#..