Gang Headquarters... You can extend the headquarters and build different things around it, using GPs... like a weapons factory, a gym with more effective trains for gang members, or even a car garage, where you can take cars from, in order to travel for free to other districts... a deposit where you store the weapons and money, which can be robbed by attacking gangs... A science lab, where you can forge more powerful weapons, or even pimp the ones that you already have, by adding different parts to a weapon, in order to make it unique and more powerful. The ideas can continue, but I invite you all to bring up your ideas