Creating a interface similar to a furnace

[DashAhead]

So I'm planning on creating a mod where when a gem and tool are put together, then the tool absorbs the gem's energy and gets a special effect. How can I create an interface similar to the furnace with 3 squares in total?

[Mecblader]

Just look at the minecraft furnace code or just google a tutorial on how to make a furnace and pick and choose the things you want.