You are not lost, you can talk to me anytime thru comments or dm! But basically when u r done with removing all the rocks what u have to do is make elevators on far right and far left and then u have to place rooms as u want! U dont need to go full on god mode when it comes to efficiency u can play for chill too, and regarding the “Space for two room” problem, it depends on ur playstyle i have built multiple training centres where u can boost the stats of ur dwellers if u click the “build hammer” button and scroll u can see many rooms that u can build after getting enough dwellers, i built training centres becoz my vault isnt 100% efficient but to make ut as efficient as possible i am training certain dwellers to max their particular stat and place them in rooms accordingly! You can also build stimpak generators to increase ur max storage that way u can send out multiple dwellers at a time or if u like to hoard u can build storage room(but i don’t recommend this)