I also use square patches. They have always worked just as well for me as a round patch in every caliber, gun, load combination that I've ever tried...
...AND they are a whole lot easier to make with that blue striped pillow ticking. Just follow the appropriate stripe on the vertical cuts, and then while keeping a ruler or sample patch as your gauge, you can replicate the size almost exactly on the horizontal cuts.
A good paper cutter might make this more accurate and easier to do. But that costs money as well. It's always good to improvise with commonly available materials, as you can usually find them in less common places. It would be wise to invest in a good all metal (and sharp!) pair of scissors too.
Usually a patch's dimensions are about 3 to 3 1/2x the diameter of the ball. So for a .36 cal that would make it about 1 1/8 - 1 1/4 inches diameter on a round patch... or the same number going across both both directions on a square patch.
The copper tubing would also work, but you have to make a handle for your punch or you are going to end up with some awfully sore (and maybe cut) fingers and palms.
Shoot Wisely and Safely!
WV_Hillbilly