What can I build in Minecraft?

Eq
5

Anything, complicated too, but it should have something to do with Redstone

Ma

You could build a (semi-) automatic farm

Th

Build a machine that brings your world to crash xD

le

Try to build a 9x9 redstone door.

Ag

If it is supposed to be very complicated, use a working calculator.

to

It's not that difficult, but with a lot of people watching, piston, sand and funnels you can build something like an earthquake simulator. Just try a little with the circuits