Marble is overdone, maybe add some other stuff than marble.
Firstly, for more detail you could add some windows, you’ve got a lot of empty space. You could also add some color and material variation instead of white concrete/marble. I could see something like a gold metal trim on the edges and the bank sign getting a color change.
You should add more protecting the safe/vault.
I suggest you add more detail both in and outside the bank. Looks good though! 
Everything on the outside is the same color I recommend changing the pillars color and also making the roof a bit more flat banks usually don’t have a pointy roof.
I was going for something like
It looks like the top is flat with the house-like shape being on top of the top, slightly smaller.
Okaay, so I see where you were trying to get to, however, more more and more detail, inside just looks empty… Even though it has stuff in it, it just feels as more should be added, like the bank counters, reception desks, security cameras, etc… Inside the vault, you should try to randomize the moneybags, and cash, not like them being like perfectly reflected on each side. If you understand what I mean.
Gold bars and cash should be on an table in the middle or something, there should be some counters that like hold other stuff, just like the one in payday 2 if you ever played that game.
Overall, bank looks good, if this is your first build, then, awesome start!
Also, here, I made an model, to represent what was I talking about, it took me like 25-45 minutes to make, of course if you are trying to make the it the jailbreak like style, then this model is not for you, I made this more realistic looking, of course its not perfect, nor the room is not fully finished, but you can take some inspiration from it, and if you want, you can even take stuff from it. I wont bother, most of the meshes (robux and robux bags) are made by roblox, and other stuff like gold bars are made by me, so as I said, I won’t bother if you use any of it. My intent is for you to possibly take some inspiration.
Model: https://www.roblox.com/library/5066735679/Bank-Interior-Example
You should add more detail inside and outside. It looks pretty plain and easy to make, details will help a lot.