I cannot take credit for the initial design of the weapon myself, that belongs to the mind that is Nighthawkinlight, but I can take credit for making it extreme. First thing first you will be needing to assemble the Bull Pup gun which is very well described here
. Secondly you will be needing an air source
that is easy portable and has a high capacity, you could make one yourself, and in fact Nighthawkinlight also has a tutorial
for that too. Though I would suggest against it, because even though it looks ridiculously cool it doesn't have the air capacity that a manufactured 5 gallon air tank has, yet I would love to see his design made professionally out of metal and if that was done it could be used in a number of applications ranging from Airsoft to paintball to construction. But i digress, once you get an air tank, whatever one you deiced on using, you will need a backpack to carry it in. I'd use what you have available but if you need to get one id suggest obtaining an old military style canvas bag, so you look like a boss tearing up the battlefield with your homemade widow maker.