You want to make only as much as what they will eat in one day, and that does take some trial & error in the beginning - so start small. I started with a rain gutter that was already on hand, but the vinyl turned out to be hard to clean. Eventually I added trays that rest perfectly in the gutter. The trays are the bottom half of those trough-style chick feeders, which are plastic, so they're much easier to clean! Someone here on BYC made this: (sorry I didn't note the owner!)
View attachment 2419044