DCF77 (AM 77.5 kHz) receiver in discrete components?
I was looking into it some time ago and it seems that the 77.5kHz band is very noisy (SMSPs and stuff) and it makes it quite difficult to build a good receiver for DCF77. Most projects are based on ready-made modules.

If you want to make something simple try building an analog AM receiver for local radio broadcasts. It should be easier (the signal will be stronger) and there are plenty resources on the net.

The Radio Spectrum Monitor may also be interesting to you albeit it is much more advanced project.