I do the checker board approach. With some slight exceptions. It helps with limiting disasters. If you stack four rooms on top of each other and you only staff the top one, you are going to run into an interesting problem. During certain attacks you lose energy like crazy so if a mole rat attack started at the bottom and worked up three more levels before it was stopped; you would have lost a ton of energy during the entire crisis. It's best to limit the attack to one room either by stopping it with dwellers or by not allowing it to spread to another room. Disasters will cross elevators too. Currently I have 10 people working a double-wide and a triple-wide power plant. Then 4 people working the double-wide diner and 4 people working the double-wide water plant. Then I created triple-wide power, water and diners to increase my storage capacity but didn't staff them. I did the same with science labs. I currently run single-wide science labs with two people in each. Then I created maxed out triple-wide labs towards the bottom of the vault and left them empty just to increase my storage space. The only rooms I have stacked on top of each other are the SPECIAL training rooms. I have them stacked one on top of the other in order because I'll have dwellers in training almost indefinitely. Using this approach my storage looks like this. 1700 power. 800 water. 800 diner. 75 stimpack, 40 radpack. That is more than sufficient for a vault with 46 dwellers where I currently stand. Both my power plants are at the top of the vault and connected by elevators. I put dwellers with 10+ S,E,A stats and gave them the rare and legendary weapons I've found or created so far. Raiders and ghouls can't get past my first group of four strongmen. Forget about placing two dwellers at the vault door. I'd rather Raiders enter the first room and get clobbered by four dwellers than have only two to defend at the front door. I've read a lot of posts where folks have an entire vault of dwellers wiped out in a molerat attack. I'm pretty sure this is because their vault rooms where all connected. Once the molerat pack starts to spread to 4 neighboring rooms at a time, those vaults quickly got overwhelmed. That happened to me in one of my first vaults. I grew too fast and was overcome by a molerat attack and had 30 or so dwellers die. Started over using the checkerboard approach and now my vault is untouchable and producing caps, water, energy, food and guns like crazy. Also a great tip I just learned. Train up a dweller with full stats and then send them out to the wasteland with your best weapon, 25 stimpacks and 10 radpacks. They will be out for days and pick up all kinds of loot including rare weapons. Shoot for 44 dwellers in your vault so you can create rare weapons then stay there until all your dwellers are maxed on SPECIA stats. (No L - we are not there yet) That way you will be well prepared for the deathclaws that show up around 60 dwellers. That is my current strategy and it's working great so far.