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It depends on your patience. I bought a second hand aluminium greenhouse (good quality Halls one, got lucky at £150) and spent an afternoon with me + 1 dismantling it. Transported it 20 miles and then spent a different morning putting it back together with same person. We put masking tape on each glass panel and took photos etc, but in reality most panes were the same size and clipped in anywhere with simple metal peg-like fastenings. Only one broken pane of glass. So if you have a friend or two and they are happy to help, it's all totally doable if you have instructions and patience and a morning.
TL/DR: DIY
Aluminium greenhouse assembly. What does the hive mind think - DIY or pay someone?