Used Pro-Seal glazing system kit for skylight or greenhouse. Designed for use with three 34 x 76 x 5/8" thick insulated glass units. White finish. Assembled dimensions are 9-0 wide x 6-8 high. This kit cost $530 from Abundant Energy:
http://www.abundantenergyinc.com/price.htm
Kit includes all extrusions, gaskets, screws, bolts, stops, etc. except for the foam tape, caulk, and flashing. You would need 16+ feet of foam tape, white silicone caulk, flashing, plus the glass units, to complete the job.
The glass rests on gaskets all around, and above the glass there are gaskets running vertically, and horizontally across the top only. The beveled purlins (the horizontal cap pieces across the bottom) are designed to seal with foam tape plus caulk, rather than gaskets. The damaged foam tape, which is visible in the photos, will need to be cleaned off and replaced.
I have personally built a greenhouse with a system identical to this one, and I was quite happy with it.
$300/best offer
Here are the design/construction guidelines: http://www.abundantenergyinc.com/design.htm