Designing and making DCC equipment is non trivial, but not beyond many hobbyist developers. A DCC decoder will require a microcontroller to decode the DCC signals, then software and interface circuits to control whatever is needed. For a loco decoder, for example, a set of power mosfets typically gate on or off the motor power feed to regulate its speed.
A challenge for decoder construction will be physical size. One of the biggest changes noticed by the users in DCC over the last 7 years has been ever-shrinking decoders. This is brought about by using surface mounted components, assembled in quantity by robots. It is hard to do this at home.. but some have managed.
There is a lot of material on the internet to get you started, if this appeals.
