I got a 4x8 sheet of 6mm I used for a coldframe I built , similar to what you are describing, for around $45 locally at Martin's Produce Supply in Shippensburg, PA ...

Shipping will kill you ...

They also had the aluminum "h" channel to attach it to the frame ...

tikifarmer,

Thanks for the info.

Martin's is a 3hr drive from here - probably not cost effective (grin).

Can you give me any more info on the sheet you purchased so that I can find same/similar locally? Is there a manufacturer name or product #, etc.

Is it polycarb or what other material?

More info is better - I like the price, just not the location. 4x8' would be brutal to ship.

How does the H channel work?

Thanks again.

Andrew

This is the stuff I used (polygal). It is double wall polycarbonate . It was the 8mm thickness ...

http://www.polygal-northamerica.com/standard_grade.php

The "h" channel screws to the top of your frame and holds the polygal in place . The polygal slips into the open end of the "h" and the crews go through the straight part of the "h" . This eliminates the need of screwing through the poly carbonate .

I hope this makes sense . If not it will once you have them in hand ...

Here is a link that might be useful: Greenhouse Glazing

I have made mine with canopy parts and 1 inch EMT conduits. The conduits are available at home depot and the likes. If you search for canopy parts on the web you will find many places that sell the connectors. I use regular 6mil plastic cover from HD. Cost of putting it together was about $150 for a 8ft by 10 feet frame about 8ft height at the center. The metal parts all come apart easily and can be assembled back in less than an hour. It has lasted for 10 years now. The plastic needs to be replaced every 2-3 years. For the sides I used the same plastic but use a stick on zipper - the kind used for making zippered doors during construction. The zippers are my doors. They are I think more than 6 ft in length. It is kind of awkward to get in and out but works for me.