This cube includes Invasion Block (Invasion, Planeshift, Apocalypse), Ravnica Block (Ravnica: City of Guilds, Guildpact, Dissension), and RTR Block (Return to Ravnica, Gatecrash, Dragon's Maze). This cube has four large sets and five small sets. Let's look at the rares I currently have. They are mostly from RTR block, then a few from Invasion and Planeshift sets, and also a few from Ravnica: City of Guilds.
Here is an example showing rares I am missing. The coverage is poor at this moment, and there is lots of room for improvement.