I think several limitations are clear:
1. Light urethane coated nylon is available for about $3.00 per yard. You won't be able to make anything cheaper than that.
2. Light urethane coated nylon is very waterproof (more than silnylon). DIY cuben won't beat it in that respect, either.
3. Light urethane coated nylon is much stronger than any laminate of a similar weight that you could make at home.
If you just see the DIY cuben project as an interesting challenge, and you don't have any intention of producing a material that is competitive in any respect with other available materials, you then have the freedom to try all kinds of things. You could apply the thinned laminating adhesive with an airbrush or spray bottle, and use light silk (0.5 oz/yard), nylon or polyester veil material (ie "tulle", 0.7 oz/yard), nonwoven kevlar (0.4 oz/yard, from composites suppliers), nonwoven nylon (0.3 - 0.9 oz/yard), nonwoven polyester (0.4 - 0.9 oz/yard), nonwoven polypropylene (0.3 - 0.9 oz/yard), or nanoseeum netting (0.7 oz/yard). Some of these stretch more than others, and none are very strong compared to woven nylon fabrics, but they are stronger than painter's plastic or Heatsheets. For the film you could use generic clear mylar, space blankets, Heatsheets, painter's plastic, window film, urethane or nylon vacuum bagging film, etc. The Heatsheets, painter's plastic, and window film won't stick to the glue well, but weak adhesion might be enough. Post your results if you decide to experiment.