Unlike Lilyanne, I've not had a good experience with my polycarbonate greenhouse which I've had since November last year and my advice would be to avoid them. I only recently got into gardening, wasn't sure I'd stick at it, so bought a cheap polcarbonate Gardman greenhouse.
The quality is awful, there are loads of gaps meaning it doesn't stay very warm once the sun goes down. The 'metal' bits, nuts, bolts and frame seem to be an alloy with strength aligned to a ripe cheddar, I sheared several bolts whilst hand tightening them. When it is windy (I live in Newcastle, to be fair we've had worse than usual recently), I regularly loose panels, some I've still not found, that's despite trying to use many clips, No More Nails and outdoor sealant, the problem is really the frame again which flexes so much because it is so weak. The flxing has warped the weak metal base, so it is no longer flush with the ground, so drafts and many creepy crawlies get in.
Gardman customer service has been nice, swift and sent me a number of replacement parts, panels, clips and the plastic door haning one that broke. But it doesn't make up for the product being so pathetic.
I'll be buying a glass, decent branded one soon and breaking this one up for cold frame parts, if i have any panels left by then.