I have received this question from a few clients, but I have 0 experience building a 24x7 SOC.
As the others mentioned this can only be established when you know more requirements.
These might include but not be limited to:
- scale/type of work involved. (I.e. how much work/ how often ?)
For a rough idea you could sketch out how the current incidents you mentioned would've been ideally dealt with, and how much work this would've taken from how many people - with generous estimates as always on time actually required.