by Markku Riihonen @ EDN Europe:
Does it make sense to design and build your own single-board computers? It used to be the sensible option for anyone concerned about matching features to production cost.
Traditionally, with your own board design, you have the freedom to add only the components that are absolutely vital to achieving the right level of functionality for the target application. But the relentless rise of the system-on-chip (SoC) device has changed that equation in a number of ways.
Should you build or buy your next single-board computer?- [Link]
i have made my own linux board
http://www.circuitvalley.com/2015/11/linux-board-homemade-pcb-design-ddr3-schematic-altium.html