A friend has a used greenhouse he'd like to sell. We've been toying with the idea of getting a relatively inexpensive greenhouse for a number of years. I have very little idea of what to look for and at when we go to look at this. It is 20x48 and will need new plastic. Other than that he thinks all the parts are there. It does need new particle board but I have no idea where that would go. Maybe he is using that in the ends? He says it has most if not all the pressure treated lumber parts. What else should I look at? Any "do"s or "don't"s when buying used? Recommendations on where to get plastic? Double vs single thickness of plastic? He does have the pump to pump the air between layers. If I don't want to go the full 48' is it possible with most setups to leave out some sections to make it shorter? Anything else I should ask but don't know to ask? I'm kind of clueless on this.