You can use Roomba 500, 600, 700 and 800 series as a base of Roomblock. They have a serial port to communicate with external computers. Notice the flagship model Roomba 900 series have no serial port, so you cannot use it.
You can see the serial port as the picture shows. Be careful not to cut your fingers or break your Roomba!
Roomba 500 series ROI connector
Roomba 700 series ROI connector