I would like to know how do you make 1/350th scale ropes? What material would you use to make the ropes out of?
Thank you.

What type of "ropes"?-- There are all kinds-- halyards, antenna, cables, hoses, etc. it would help to know what you are after. I use a combination, depending on what I want to represent. Here's a few I use: antennas are generally made from thin nylon "magic thread" or Berkshire Industries "EZ line". Occasionally I'll use 2lb or 4lb fishing Leader. Supporting lines and halyards might be made of fine wire or thread which is waxed, depending on the thickness desired. Deck ropes might be coiled from thin silk thread which is waxed. Cables are usually thicker waxed black or dark gray thread. (Waxing is done to prevent fraying and ease forming). Hope this helps answer your question.
VR, Russ

Russ,
I'm looking to make deck ropes for my U-Boat in 1/350th.

If it's just ropes (hemp) used for mooring, then a fine sewing thread would work, waxed (as noted above) to eliminate the "fuzzies".