An all-LEGO clock.

I made a clock out of LEGO, which works nicely. To any clock, there are four essential elements: the hands, the escapement, the pendulum, and the cogwheel (which enables you to lift the weights without stopping the clock). Instructions for those are provided, plus a suggestions of how to put them all together to get one working clock .

T5 made a YOUTUBE VIDEO based on this design.

Then, when you have all the parts, you may want to build the actual clock. I have not done this, but Eric Harshbarger went all the way (with his own different designs for the internals) and built a real-size Grandfather clock! And Amnon Silverstein has made one that strikes (plus gives handy links to other Lego clocks).