The point I am making is not that it is imposable to make your own it is just that it is not easy to get it right first time. Better men than me have failed at that.
That's discouraging. The implication is that there's no reliable way to design this board and be confident that it will work, other than the empirical (and pricey and time-consuming) approach of building it and seeing if it fails, then trying to figure out why.
Or pay the premium for a pre-packaged DC-DC converter, of course.
This is why electronics is an art as well as a science - well once you are in high frequency domain that is. There is no such thing as a resistor at high frequency, everything has stray capacitance and inductance. At RF frequencies a ceramic capacitor and a plastic film capacitor behave completely differently for instance. Even a simple trace on a PCB is a transmission line with impedance of the order of 100 ohms..
Actually it's still a science so long as you have the facilities for simulating Maxwell's equations for your board layout and components!