Backyard waterfalls are a beautiful landscape addition that most anyone can have. The scale of difficulty in installing your own will differ based on how complex of a waterfall you want.
The depth of one can vary based on wants and the topography of your back yard. If you want the fall of your water higher than usual then the depth is going to have to be deeper as well, which means more digging. The payoff though is a more majestic looking waterfall in your backyard.
The placement of the dirt and rocks that the water will flow over is something to be mindful of as well. Many people also put lighting, typically solar these days, around the waterfall itself to help accentuate the entire look. Well placed and angled lighting also helps with the enjoyment of the falls at nighttime.