I would not use that glass, because of that green hue. I would use: Twin-Wall Polycarbonate Sheets - Clear. The sheets are not expensive, but shipping will be. Now, if you have a store close, you can cut the 4 x 8 ft. in 4 pieces 2 x 4 ft. and transport it yourself. 8-10 mm thickness is the best, but 6 mm is ok. 4 mm only for small surfaces.

There is also www.FarmTek.com - they have twin-wall panels made by Palram, custom @$5.95 per 4' sheet and 4x8' sheets @ $41.95. Shipping seems to be $7.00 per linear ft per package up to 12' - to a maximum no. of sheets per package of 50. They also have a roll of twin-wall corrugated plastic: 8' wide; each @ $7.39 per linear ft, and a 250' roll @$6.95/linear ft. They don't say what the shipping/freight charges on that would be. You can also call them - 1-800-327-6835. While I am not sure how much they would be price-wise compared to local sources, their prices for the water filters I have bought from them seems to be competitive ($5-7 against what I priced at Lowe's a few years ago at over $15!) - they have stuff for agricultural growing and storage, so they carry everything that can come under that heading - the specialty catalogue I just got, for that only, runs to 352 pages.

szut, I can give you my experiences from Z5 in the Rockies, but that at best might be a bit similar to your locale. The short answer is yes, I would get some tomatoes now (some larger plants from a nursery/store would get you going faster than starting seeds at this point). Assuming you picked up some decent sized plants, you might be getting ripe tomatoes in 5-6 weeks. However I say this from the POV of I manage summer temps in my GH and keep it going all winter, so if you have no plans along these lines, then maybe it would not make sense to start now. However if you put the tomatoes in large pots, then they could stay outside until fall and migrate into the GH, which should give you a few more weeks to a month of season extension, even without supplemental GH heat (at least I can get that here most years). I typically leave one or two tomato plants from my summer production in the GH over the winter. They typically produce well up to Thanksgiving, and sometimes longer, although everything slows down in Dec and Jan (I add heat but do not add light so the shorter days hurt). I do have a heat storage system which helps keep the temps up without outrageous fuel bills. And my climate is typically quite sunny, which helps too. It has been too many years since I lived in the NE for me to have a good feel for how much of my experience here would be applicable to you. As Hudson says, check with some local GH folks and see what they do. But I will say that conditioning a GH for the summer is relatively cheap and easy compared to doing the same for the winter. Some fans and vents, possibly shade cloth, and water misting will do quite a bit to keep summer temps down. Good luck.

They could both be 80% transmission. But the one with a clearer view diffuses the light less. Diffusion is usually good because diffused light penetrates the leaf canopy better resulting in higher total canopy photosynthesis. Look for a number about % diffusion. I generally prefer the panels that diffuse light even more than either of those provided it doesn't lower total light transmission too much. On those you can't see much of anything looking thru but claimed light transmission can still be near 80%. In my experience and using the light meters I have all light transmission values are for best conditions only not real world values. But if you get more than 50% actual on average over all daylight conditions that's enough for almost anything and may be too much for things like orchids.