Hello Steve welcome to the forum. There are a lot of designs on the web. You just need to look around.I have built several improving on each one. I'm not certain it would fit into everybodys plans but it fit mine.
When you get right down to it they are all basically the same. A box to put eggs in that holds a certain temp, and humidity.Any way you can get it to do this isallright. Most have a thermostat of some kind most all use water, but if it will hold the temp and humidity it will hatch eggs. This forum is a good place to start looking a lot of people here have good ideas :) P.D.