greenhouse manufacturer/ supplier recommendations please

[organicartist]

I'm looking for a high sided greenhouse, something like dutch style greenhouse perhaps, metal rather than wood framework, with toughened safety glass, maximum size width 12 foot, max length 20 foot. 

Quality & price seems to vary dramatically, have had a bit of a look online, but feel overwhelmed by the sheer number of retailers.

I'd be happy to buy secondhand, but am disabled, so I would need to pay my usual handymen to collect it & assemble it.

[organicartist]