1/4 inch hardware cloth will work, check the regs for maximum length and diameter. When I was trapping and selling minnows we were restricted to 24 inch length so we used 24 inch rolls of the hardware cloth. Be sure not to exceed maximum trap diameter and cut the cloth 3 times the diameter you want to build. Roll into a tube and sew the seam with a flexible wire. If you are going to be trapping in current you only need a funnel on the downstream side, it is easier to cut and attach a flat cover on one end. The funnel end should be about 10 inches deep, with a one inch hole for the minnows to enter. I made a pattern to use for the funnel, after you get one cut to the proper size it goes faster if you use one. Cut a hole with a flap for a door to get the minnows out and you are good to go. I have used square traps also, they hold more minnows but you have to check the regs for sizes.

This is what I make

i Had made those trap for a person who wanted to get some water snake that was hanging his boat dock. He would put some live fish in it. My grandson had put some dead fish and got some crawfish.so I think if a person would put some dog food in it you get some minnow