The fabric bit from Military Mart arrived today, and I've just been looking at it. Measurements on the web site were slightly larger - I got 71x208cm. Weight is 580g, and it folds up pretty small - about 15x20cm by maybe 3cm thick. Dark olive, looks to be nylon and feels substantial enough for me not to worry about lying on it. No sign of a waterproof coating, so probably not suitable as a groundsheet (and arguably a bit too narrow).
It does indeed seem to be part of a camp bed on the basis that the longitudinal tubes along the sides each have an opening half way along to allow a middle set of legs to connect to the poles/supports in the sides. I would agree with the stated 7.5cm diameter for poles - the sleeves themselves would allow a bit more but the openings at the ends of the long sleeves are a bit smaller and limit the diameter to this. The transverse sleeves at the ends don't have the narrower openings, so could probably manage something a bit bigger, but I doubt that it would be needed. If I was making a cot bed in the woods, I'd probably seek out some 2" diameter straight poles, or maybe something that was 2.5" at the wide end, and let them taper down to maybe 1.5" with the narrower end at the feet.
To make your own, you'd need a continuous length of fabric nearly 2.5m long and about 1m wide to allow for the folding to make the pole tubes on all four sides. In online fabric buying, that translates into 3m long and 1.5m wide. It might be possible to get heavy unproofed nylon for the price of this plus postage (11 quid), but then you'd have to make it yourself. Fine if making one is what you want to do, but debateable if you're out get one on the cheap. As mentioned above, I got a Czech bedroll and a couple of smaller things in the same order, and the postage didn't go up, meaning the proportion that was postage for the camp bed fabric went down quite a bit. And it's already made.
One possible area of concern is the width. Being intended for a camp bed rather than a hammock, it is presumably meant to be quite taut. If it was set up with some sag across the width, I suspect the longitudinal poles would get in the way of the shoulders. I'm about 50cm across the shoulders, which would leave a bit of room either side once the diameter of the poles have been taken into account, provided it's reasonably taut. On the other hand, setting it up with longitudinal ropes, as in John's photos, would make the effective width greater
No idea when I'll get a chance to try it out, but if it turns out that it's too narrow after all, then at least I got some heavy nylon fabric for sensible money. Strikes me as a possible candidate for a sling chair (or two) if the cot bed idea doesn't work out.
