How to build wall folding chair?
Building the seat is easy, anyone with a reasonably complete tool set and any aptitude for construction could bang those together. The hardware, on the other hand, is another story. The hardware shown is a specialty item because of both its particular functionality and the rather extreme torsional load it has to deal with. The next concern is attaching the unit to the wall. Your wall's substructure might not be adequate, and if your seat is configured like the picture it almost certainly won't have studs where you need them (the middle would require 3 or 4 studs stacked together to catch both brackets). You may need to cut open the wall and beef up the substructure, or design your seat so it bears some of the load down into the floor thusly:

This layout could be built with dimensional stock and off the shelf hardware (lags, carriage bolts, etc.) but I have to admit it lacks the elegance of the floating bench.