Legs are constructed in 9x9x27 structures, directly next to each other (Touching)
Bodies are 18X9X27.
arms be 9x9x27 just the same.
and the head will be 18x9x13
In total you will need:
162 Right leg blocks, 162 Left leg blocks, 162 Right arm blocks, 162 Left arm blocks, 324 body blocks, 324 head blocks and a grand total of 5144 connecting blocks.
Once the actual robot is built it will need to be controlled, powered, and defended:
Defense is improved by swapping better connecting blocks for others: Say you have an entire robot made of dirt (and other bits) that's a weak robot, to make it stronger replace some dirt with obsidian blocks, or any harder material.
To control the robot is more simple: You just need a control station, to craft you will need an ender pearl (middle top), three beacons (along the bottom row), a lever (middle right), and glass in the remaining slots. Place this anywhere you want it's not important. Next you will need to go inside your robot's head and place another block: Control box, (crafted with 8 redstone blocks around an ender pearl) anywhere within the structure. Right click it and set the code. Then leave your bot and enter the control station, input the code and you have control, and can move your bot!
To power this thing is NOT a simple task. You will need to place (a) furnace(s) into the body of your bot, and fill them with coal. Alternatively one can make generators by smelting a furnace in a furnace. This new furnace when placed will not cook food, but will instead consume coal, or redstone, or lava, and move your robot. If all your furnaces cut out your robot will power down. To access the inside of your robot easier, one can place doors along the outside: NOTE no one can enter the bot when in motion.
Controlling the bot is simple, it walks around as a GIANT player made of the individual blocks. WASD to move, space to jump (Landing will make explosions), punching will create explosions too, if one right clicks, the player launches explosive rays (like missiles) from their face.
Making the mod is simple, acquiring the resources for the actual gameplay? NOT AT ALL. The robot is an end-game work and the mod is meant to be paired with mods that allow easy-aquirization of resources.