If I am not mistaken a Clan level 2 can already auction for a Clan Hall. If that is a wrong info (for which I apologize), then I am 100% sure that a Clan level 3 can auction for it. Level 4 needs a quest and everyone can have a Clan Hall before questing begins. So level 3 is definitely giving you a chance to auction for your Clan Hall.
If you have a chance and can spare that 20.000.000 adena + 10.000.000 adena per week, be sure to grab yourself that Clan Hall as soon as possible. Trust me, you won’t regret it!
It is not that you do not understand, it is that you do not even question.