imagine going inside a building, Spawning zombies inside and then making the zombies come to you, And you get a gun with ammo to kill em all, Well there are games like gmod (paid), gravitymod (just missing a lot of stuff) and RSandbox which is only avaliable for mobile. I forgot to mention there is glass city alpha v1 which hasnt gotten updated in a long time. So if you could try to remake it and add more stuff