Nice pics! I have made a few of these larger shelters too, and usually they are on a favorite trail where I return to often, and are a bit more permanent than a one-nighter setup. For example, I would set something like this up at a location where I would make a basecamp to store some equipment and unload some of my pack before making a climb. I might stay farther up the mountain for a night or two, then return to the basecamp confident the shelter would still be in great shape. Some have lasted many years and stored containers and fuel from previous trips. It's fun to make and quite useful.
Concerning the rope used, I go with the white nylon rope you you normally see used as starter rope on lawnmowers. It is rot-resistant, won't bind when wet, is light, and is remarkably tough. It can be purchased cheap at the harware store either from bulk rolls, or in bags of various lengths. It isn't overly expensive either.
One particularly large basecamp shelter I once made was covered in living moss that I carefully harvested in large sheets from the forest floor. The roof was angled away from the sun, so the moss actually continued to thrive for several years (might even still be growing for all I know, heheh). The moss made for an almost impermiable roof, and never leaked a drop even through a deluge of biblical proportions. It was also an amazing insulator that stood up to several snowy winters without showing any signs of weakening.
