Step 1: Basic Structure
you need a rocket launcher with rocket. connect the rocket launcher to the 2 14x1s. Put a 4x14 flat on top or make a substitute on it then add a longer trigger and 2x2 brick on top of a 4x2 brick underneath then put together.
Step 2: Barrel and Handle
add the barrel peices and lower cap to finish barrel. the make a handle to your hand size and comfort. Then add decoration. you are done.