So you want to build your own Arduino driven Mecanum wheel robot? The Mecanum Wheel Arduino Robot Kit has you covered. It comes with a 4-wheel drive system, 4 coreless 12V DC motors, Arduino 328 microcontroller board, and an IO expansion board.
The robot has an aluminum body and can move in any directions. You can program it in C and C++. It can also climb 45 degree slopes.