Greenhouse/ Arbor against a wooden fence.

I am building a high wooden fence sheathed in rough cedar planks, to replace the chain link fence that is currently there. My wife wants me to build an overhead an arbor for the grapes that had been growing on the chain link. I think this is fine idea , but I would like to make it a greenhouse frame as well.

I am wondering what matirial to use for the rafters. PVC, steel pipe, wood studs, treated wood,metal studs,what might be best?
It needs to be kinda stiff, my design involves the tail ends of rafters cantalivered out almost 5 feet.
I am also unsure of spacing, 24" ,16"what do you think?

I might fill the spaces between the rafters with chain link or snow fence, what ever the wife will go for. I have used this before to keep tarp covered car ports from pooling water and collapsing. I envision trimming away any growth that stuck above fencing at the end of the growing season, and rolling the vinyl sheeting down from the peak of the structure. Sound reasonable ?
One thing I worry about is screwing up the vines that would live under the plastic sheeting seasonally,throwing of their sense of season.

The fence is almost done. The greenhouse frame/arbor will cover a raised bed about 20' long, an access path along side that , and some 55 gallon Sub Irrigated planters lining the other side of the access path.

I want to plant Austrian Winter Pea for the winter, then I want to spam it with comfry roots come spring.
The bed has produced years of volunteer tomatoes, one bumper crop of grapes, sapling sized j chokes, struggling Hardy kiwi and lots of bind weed.
I want the comfrey to help keep everything but the grape and kiwi in check. Starts and propagation will occurs in SIP containers, to be moved come spring.
I will add some gutters to the fence, when I get some money for them, and I hope to grow strawberries, peas, greens, etc.
If there is is any heating other than solar gain in the 55 gallon sips, it will by pumping heat into the ground beneath the access path, be that solar heated air pumped from where it gathers at the peak of the structure, or via rocket stove.

So anyway, what should I use for my rafters, and at what spacing? Any other advice?

you could use wood but it sounds like you would need to go with 4x4's for the structure to be fully stiff and sound.
This would mean either using timber frame or heavy metal brackets, depending on your abilities in carpentry.

I would probably try to locate some aluminum either I-beam or C-channel to build the frame with.

There are several things to consider when building a green house: 1) is the glazing going to be glass.
2) length, width, height of structure
3) length of time you expect it to last.