Best material to use for making own couch slip cover?

For wear and tear purposes, a medium to heavy weight upholstery fabric would be ideal. If it only gets light use, you could go with a lighter weight fabric. Be sure to check the cleaning instructions.

It really depends on where it will le located and what it's function is. If it is in a casual setting, use a heavy duty and washable fabric like cotton, linen or duck (and put in zippers on the cushions to put in the washing machine). If it is more formal, use wool, velvet, brocade, or a suede-like fabric.

It depends on how fitted you want it and how well you sew. Use a light-weight woven upholstery or drapery fabric* if you want it fitted or want to tie it and you don't want it to stretch, and you know how to sew and take your own measurements. A medium- to heavy-weight knitted fabric would work if your sewing skills are limited and you're satisfied with tucking and tying the cover onto the piece of furniture, Knitted covers require more fixing, re-tucking. I would mention, though, that unless you have a very good coupon or an economical fabric store or you want a fitted slipcover, buying one will probably be substantially cheaper than making one. I would look at what's available in stores and online before buying fabric.

*regular dress fabric is too thin/light-weight for the stress fabric on furniture gets

Good info source... https://www.craftsy.com/blog/2015/08/fabric-for-slipcovers/