United Kingdom 
We have a concrete greenhouse base built very solidly on a sloping site. Unfortunately the builder made it 1920 x 2530 and I can't find a greenhouse to fit, preferably an 8 x 6 foot one. They all seem to be a few centimetres bigger! Does anybody have any advice or know of a suitable greenhouse for us?
18 Apr, 2011
Answers
Several of the greenhouse companies say (on google) that they can supply 8x6 or any size why not contact one and see.
The other thought I had was you could lay a frame of concrete or wood sleepers around the base to make it a bit bigger.
19 Apr, 2011
Try Ebay there seems to be lots on there from only 99p.
21 Apr, 2011
Previous question
To have something built to size out of wood and glass is going to cost a fortune, So why not build a polytunnel. You can build them to whaterver size u want.
We used this idea and it worked out about £400 cheaper than a made to measuer one we bought years before.
Here's the link. Copy and paste.
http://www.overthegardengate.net/UserPages/pp_view.asp?FName=Polytunnel&Page=1
19 Apr, 2011