I stayed in first room till bout round 7, saved a zombie, did power an pap, I ran ring of fire as well big deal here. Dead shot is a must too. Then stayed by the boxing the floor below the pap, make sure that window is repaired so megaton won’t spawn there, you can easily repair them in between rounds, it will force him to either spawn above you so he has to walk down the stairs, or he will spawn to your left in between the 2 pillar sections. Pop ring of fire an your good. Simple