The Hustle Castle Throne Room is probably the most important room you have as it will have to be upgraded before everything else. As you improve the Throne Room new rooms will become available as it’s level gets higher and you’ll be able to improve existing rooms. You can see whats unlocked when by going through the tabs in the Market.
Since the Throne room is more of a decoration you can keep it on the outskirts of your building area so dwellers can reach more used areas faster.
There are 2 ways of accessing the castle editor. This first is by tapping on the Throne Room while the second way is to long press anywhere on the screen in the rooms area. With the editor you can move the rooms around how you like them when ever you want to. They can even be moved while upgrading or producing resources.
When some rooms are placed next to each other they can merge and become a bigger room. To do this they just have to be the same level and type before they will combine automatically when placed next to each other.
You can find clatter on the empty castle space that takes time and gold to remove. This can be a good source of free diamonds if you keep removing them all and letting new spots appear.
When merging rooms you can break them into pieces again so upgrade cost will be less and easier to manage. To do this you’ll have to place all sections away from each others and remember to hit the save button.